Infectious Disease and Microbiology – Hantavirus Group

Overview

Hantaviruses are enveloped, segmented, negative-sense single-stranded RNA viruses that cause two major human disease patterns: hantavirus pulmonary syndrome (HPS), also called hantavirus cardiopulmonary syndrome, and hemorrhagic fever with renal syndrome (HFRS).

The clinical syndrome depends largely on the viral species and geographic region. In the Americas, hantaviruses such as Sin Nombre virus are particularly associated with severe pulmonary disease, whereas Eurasian hantaviruses such as Hantaan, Seoul, Puumala, and Dobrava-Belgrade viruses are primarily associated with HFRS.

Classification

Hantaviruses historically belonged to the family Bunyaviridae but are now classified within the family Hantaviridae.

Multiple hantavirus species are capable of causing human disease.

Microbiologic Characteristics

Hantaviruses are:

• Negative-sense single-stranded RNA viruses

• Enveloped

• Characterized by helical nucleocapsid symmetry

• Equipped with a three-segmented RNA genome

The three RNA segments are conventionally designated:

L = Large

M = Medium

S = Small

Epidemiology

Human hantavirus infections are relatively rare, but they can produce severe and potentially fatal disease.

The viruses are maintained primarily in rodent reservoirs, with different hantavirus species associated with particular rodent hosts and geographic regions.

Transmission

Humans usually acquire infection through exposure to infected rodent excreta.

Transmission commonly occurs through:

Inhalation of aerosolized virus from rodent urine, feces, or saliva

Exposure can occur while:

• Cleaning rodent-infested buildings

• Entering poorly ventilated structures containing rodents

• Handling contaminated materials

• Working or camping in rodent-infested environments

Major Clinical Syndromes

Hantavirus infection produces two major syndromes:

Hantavirus Pulmonary Syndrome (HPS)

Predominantly associated with hantaviruses of the Americas.

Hemorrhagic Fever With Renal Syndrome (HFRS)

Predominantly associated with hantaviruses of Europe and Asia.

Hantavirus Pulmonary Syndrome

Sin Nombre Virus

Sin Nombre virus is the classic cause of hantavirus pulmonary syndrome in the United States.

It became particularly recognized after an outbreak in the southwestern United States.

The historical term Muerto Canyon virus was initially used for the virus subsequently named Sin Nombre virus.

Clinical Course of HPS

The illness often begins with nonspecific symptoms such as:

• Fever

• Severe myalgia

• Headache

• Malaise

• Gastrointestinal symptoms

This initial febrile phase may be followed by rapidly progressive cardiopulmonary disease.

Pulmonary Phase

The major complication is:

Rapidly progressive pulmonary edema and respiratory failure

Patients may develop:

• Cough

• Dyspnea

• Hypoxemia

• Bilateral pulmonary infiltrates

• Noncardiogenic pulmonary edema

• Respiratory failure

Severe disease can progress rapidly to shock.

Cardiovascular Involvement

HPS can involve not only the lungs but also the cardiovascular system.

Severe cases may develop:

• Hypotension

• Myocardial dysfunction

• Shock

For this reason, the term hantavirus cardiopulmonary syndrome is also used.

High-Yield HPS Pattern

Rodent exposure in the Americas

• ●

Fever and severe myalgia

• ●

Rapidly progressive pulmonary edema

• ●

Hypoxemic respiratory failure

→ Think hantavirus pulmonary syndrome

Hemorrhagic Fever With Renal Syndrome

Overview

HFRS is primarily associated with hantaviruses circulating in Europe and Asia.

Important viruses include:

• Hantaan virus

• Seoul virus

• Puumala virus

• Dobrava-Belgrade virus

Severity varies substantially according to the infecting virus.

Clinical Manifestations of HFRS

Patients may develop:

• Fever

• Headache

• Myalgia

• Thrombocytopenia

• Hemorrhagic manifestations

• Hypotension

• Acute kidney injury

• Proteinuria or hematuria

Renal involvement is a defining feature.

Hantaan Virus

Hantaan virus is classically associated with more severe hemorrhagic fever with renal syndrome, particularly in East Asia.

Disease can include substantial vascular leakage, hemorrhage, hypotension, and renal dysfunction.

Puumala Virus

Puumala virus generally causes a milder form of HFRS, often referred to as:

Nephropathia epidemica

Renal abnormalities remain prominent, but the overall disease is typically less severe than classic Hantaan-virus-associated HFRS.

Seoul Virus

Seoul virus can cause HFRS and is notable for its association with rats.

Because its rodent reservoir has a broad geographic distribution, Seoul virus infections are not restricted to a single region.

Prospect Hill Virus

The source includes Prospect Hill virus among hantaviruses.

However, it is important to distinguish hantaviruses known to cause established human disease from those primarily identified in rodent reservoirs. Prospect Hill virus has not been a major established cause of classic human HFRS.

Diagnosis

The source lists:

• Cell culture

• Serology

In clinical practice, hantavirus diagnosis is more commonly based on:

• Serologic testing for hantavirus-specific antibodies

• RT-PCR or other molecular methods in appropriate settings

Routine viral culture is generally not the main diagnostic approach.

Treatment

Management is primarily supportive and depends on the syndrome.

For HPS, treatment may require:

• Intensive monitoring

• Oxygen supplementation

• Mechanical ventilation

• Hemodynamic support

• Management of shock

Severe cardiopulmonary disease may require advanced critical-care support.

Ribavirin

The source describes an intravenous ribavirin regimen that had been investigated, particularly for HFRS.

However, the source also notes disappointing early results in the United States.

Ribavirin should therefore not be interpreted as a universally effective treatment for all hantavirus syndromes, particularly HPS, where management is predominantly intensive supportive care.

Prevention

Prevention focuses primarily on avoiding exposure to infected rodents and their excreta.

Important measures include:

• Rodent control

• Preventing rodents from entering homes and workplaces

• Safe cleanup of rodent-contaminated environments

• Avoiding activities that aerosolize dried rodent urine or feces

• Appropriate protective precautions during high-risk exposure

Isolation – Important Correction

The source recommends:

“Strict isolation during the entire illness.”

This is not a general requirement for all hantavirus infections because most hantaviruses are transmitted from rodents to humans rather than from person to person.

A notable exception is Andes virus, for which person-to-person transmission has been documented.

Therefore, infection-control precautions should depend on the specific hantavirus and epidemiologic circumstances.

HPS vs. HFRS

Hantavirus Pulmonary Syndrome

→ Primarily Americas

→ Sin Nombre virus is classic in the United States

→ Pulmonary capillary leak

→ Pulmonary edema

→ Respiratory failure

→ Shock may occur

Hemorrhagic Fever With Renal Syndrome

→ Primarily Europe and Asia

→ Hantaan, Seoul, Puumala, Dobrava-Belgrade viruses

→ Hemorrhagic manifestations

→ Thrombocytopenia

→ Acute kidney injury

High-Yield Clinical Pattern – HPS

Southwestern United States

• ●

Rodent exposure

• ●

Acute febrile prodrome

• ●

Rapid pulmonary edema and respiratory failure

→ Think Sin Nombre virus causing hantavirus pulmonary syndrome

High-Yield Clinical Pattern – HFRS

Rodent exposure in Europe or Asia

• ●

Fever

• ●

Thrombocytopenia/hemorrhagic manifestations

• ●

Acute renal failure

→ Think hantavirus-associated HFRS

Exam Essentials

Virus group: Hantaviruses

Family: Hantaviridae

Genome: Negative-sense single-stranded RNA

Genome structure: Three segments – L, M, S

Envelope: Present

Reservoir: Rodents

Typical transmission: Inhalation of aerosolized rodent excreta

Major syndromes: HPS and HFRS

Classic U.S. virus: Sin Nombre virus

Sin Nombre syndrome: Hantavirus pulmonary syndrome

Major HPS complication: Pulmonary edema and respiratory failure

Hantaan virus: Severe HFRS

Puumala virus: Generally milder HFRS/nephropathia epidemica

Seoul virus: HFRS; associated with rats

HFRS hallmark: Acute kidney injury ± hemorrhage

Diagnosis: Primarily serology; molecular testing can also be used

Treatment: Mainly supportive

Ribavirin: Historically investigated, particularly for HFRS; not established as effective therapy for HPS

Prevention: Rodent exposure control

Person-to-person transmission: Generally absent; Andes virus is an important exception

Key clinical pearl: Hantaviruses are three-segmented, enveloped, negative-sense RNA viruses transmitted primarily from rodents. For examinations, separate the two classic syndromes: Sin Nombre virus in the Americas → hantavirus pulmonary syndrome with pulmonary edema and respiratory failure; Hantaan and related Eurasian viruses → hemorrhagic fever with renal syndrome characterized by acute kidney injury and possible hemorrhage.

Infectious Disease and Microbiology – Hansenula Species

Overview

Hansenula species are yeasts that only rarely cause human infection. When clinically significant disease occurs, it is usually opportunistic and is more likely in immunocompromised patients or those with other major underlying conditions.

Reported manifestations include fungemia, endocarditis, meningitis, and mediastinal lymphadenitis.

Important Species

The source lists:

• Hansenula anomala

• Hansenula polymorpha

The taxonomy of these yeasts has changed over time, and older Hansenula names may appear under different genera in modern classifications.

Taxonomic Considerations

An important historical reclassification is:

Hansenula anomala → commonly known as Wickerhamomyces anomalus

Older literature may also use the name:

Pichia anomala

Therefore, Hansenula anomala, Pichia anomala, and Wickerhamomyces anomalus may appear in literature describing the same or closely corresponding organism under different taxonomic systems.

Microbiologic Characteristics

Hansenula species are:

• Yeasts

• Uncommon causes of human disease

• Capable of causing opportunistic invasive fungal infection

They should be distinguished from the much more common pathogenic yeast Candida.

Epidemiology

Human infection is:

Rare

The supplied material appears to have the epidemiology and diagnostic headings transposed: culture and identification in biopsy specimens are diagnostic methods, whereas rarity describes the epidemiology.

Risk Factors

Invasive infection is particularly important in patients with:

• Immunosuppression

• Serious underlying disease

• Prolonged hospitalization

• Intravascular devices

As with other unusual yeasts, recovery from a normally sterile site should be evaluated carefully for evidence of genuine invasive disease.

Fungemia

One of the major reported manifestations is:

Fungemia

Bloodstream infection may occur in vulnerable hospitalized or immunocompromised patients.

Possible clinical findings include:

• Persistent fever

• Sepsis

• Positive blood cultures for yeast

• Evidence of an intravascular or disseminated source

Endocarditis

Hansenula species can rarely cause fungal endocarditis.

Endocarditis should be considered when fungemia is persistent or accompanied by:

• Cardiac valve abnormalities

• New or changing murmur

• Embolic manifestations

• Echocardiographic evidence of vegetation

Fungal endocarditis is a serious invasive manifestation.

Meningitis

Rare cases of meningitis have been associated with Hansenula species.

Diagnosis depends on compatible neurologic findings together with recovery or identification of the organism from appropriate clinical specimens.

Mediastinal Lymphadenitis

The source also describes:

Mediastinal lymphadenitis

This manifestation is reported particularly in immunocompromised patients.

Because mediastinal lymphadenopathy has many infectious and noninfectious causes, tissue sampling may be important for establishing the diagnosis.

Diagnosis

Diagnosis is based on:

Culture

and

Identification of the fungus in clinical biopsy specimens

The appropriate specimen depends on the clinical syndrome.

Blood Culture

For suspected fungemia:

Blood cultures

may demonstrate the yeast.

Repeated recovery from blood, particularly in a symptomatic high-risk patient, supports clinically significant bloodstream infection.

Tissue Biopsy

For localized or deep-seated disease, biopsy can provide:

• Histopathologic evidence of fungal infection

• Material for fungal culture

• Confirmation that an unusual yeast represents tissue-invasive disease rather than colonization

Treatment

The source lists:

Intravenous amphotericin B

as the principal treatment.

It may be administered:

With or without flucytosine

particularly for serious invasive disease.

Treatment Considerations

Because Hansenula infections are rare, clinical treatment data are relatively limited.

Management of serious infection should consider:

• Site of infection

• Severity of illness

• Species identification

• Antifungal susceptibility when available

• Immune status

• Presence of infected intravascular or prosthetic material

Source Control

When fungemia is associated with an intravascular catheter or other infected foreign material, appropriate source control may be important.

For complicated infections such as endocarditis, combined medical and procedural management may be required.

High-Yield Clinical Pattern

Immunocompromised or medically complex patient

• ●

Persistent fungemia

• ●

Unusual yeast isolated from blood

• ●

Possible endocarditis or disseminated disease

→ Consider Hansenula species, particularly organisms now classified as Wickerhamomyces

Exam Essentials

Genus: Hansenula

Type: Yeast

Important species: H. anomala, H. polymorpha

Frequency: Rare human infection

Important modern name: H. anomala → Wickerhamomyces anomalus

Alternative historical name: Pichia anomala

Major infection: Fungemia

Other invasive infections: Endocarditis, meningitis

Additional manifestation: Mediastinal lymphadenitis

Major host association: Immunocompromised patients

Diagnosis: Culture + identification in biopsy specimens

Treatment in source: IV amphotericin B ± flucytosine

Management principle: Consider antifungal susceptibility and source control in invasive disease

Key clinical pearl: Hansenula species are rare opportunistic yeasts that can produce fungemia and serious invasive disease in immunocompromised patients. Hansenula anomala is an older name for the organism now commonly called Wickerhamomyces anomalus, so recognizing the taxonomic change is important when interpreting older infectious-disease literature.

Infectious Disease and Microbiology – Haemophilus Species

Overview

Non-influenzae Haemophilus species are small, fastidious Gram-negative coccobacilli that occur worldwide. Many colonize the upper respiratory and oral mucosa, but they can occasionally cause invasive disease, particularly bacteremia, endocarditis, pneumonia, meningitis, brain abscess, and soft-tissue infection.

Certain species have especially important clinical associations. Haemophilus aegyptius is associated with conjunctivitis and historically with a severe purpuric septic syndrome, while some species formerly classified as Haemophilus are important causes of HACEK endocarditis.

Important Species

The source lists:

• Haemophilus aegyptius

• Haemophilus aphrophilus

• Haemophilus haemolyticus

• Haemophilus parahaemolyticus

• Haemophilus parainfluenzae

• Haemophilus paraphrophilus

• Haemophilus segnis

Several of these organisms have undergone taxonomic reclassification.

Important Taxonomic Changes

Older microbiology references may use Haemophilus names that are no longer preferred.

Notably:

Haemophilus aphrophilus → Aggregatibacter aphrophilus

Haemophilus paraphrophilus → now included within Aggregatibacter aphrophilus

Haemophilus segnis → Aggregatibacter segnis

These changes are particularly important when studying HACEK organisms and infective endocarditis.

Microbiologic Characteristics

Haemophilus species are generally:

• Gram-negative coccobacilli

• Fastidious organisms

• Facultatively anaerobic, although older sources may describe them as aerobic

• Associated with human mucosal surfaces

Different species have different requirements for X factor (hemin) and V factor (NAD), which can assist laboratory identification.

Epidemiology

These organisms have a worldwide distribution.

Many species colonize the:

• Oropharynx

• Upper respiratory tract

• Oral cavity

Infection frequently develops when organisms invade beyond their normal mucosal habitat.

Bacteremia

Non-influenzae Haemophilus species can occasionally cause bacteremia.

Bloodstream infection may occur:

• With endocarditis

• During severe respiratory infection

• In immunocompromised patients

• As part of systemic sepsis

Persistent bacteremia should raise concern for an endovascular focus such as infective endocarditis.

Upper Respiratory Tract Infection

Some Haemophilus species can cause or participate in:

• Pharyngitis

• Other upper respiratory infections

• Respiratory tract colonization with subsequent invasive disease

Because several species may colonize the respiratory tract, culture results should be interpreted together with the clinical syndrome.

Epiglottitis

Although H. influenzae type b is the classic Haemophilus associated with epiglottitis, other Haemophilus species have occasionally been implicated.

Epiglottitis remains an airway emergency because rapidly progressive swelling can cause upper-airway obstruction.

Pneumonia and Chronic Bronchitis

These organisms may cause:

• Pneumonia

• Exacerbations of chronic bronchitis

• Other lower respiratory tract infections

Respiratory disease is particularly relevant in patients with underlying pulmonary abnormalities.

Soft-Tissue Infection

Rare soft-tissue infections may occur when organisms gain access through disrupted mucosal or skin barriers.

Deep specimens are generally more useful than superficial cultures for determining whether an isolate represents true infection.

Endocarditis

Important Clinical Association

Some organisms historically classified as Haemophilus are particularly important causes of infective endocarditis.

This includes organisms now classified within Aggregatibacter.

These organisms belong to the clinically important HACEK group.

HACEK Organisms

HACEK refers to a group of fastidious Gram-negative organisms associated particularly with infective endocarditis:

H – Haemophilus species traditionally included in the group

A – Aggregatibacter species

C – Cardiobacterium hominis

E – Eikenella corrodens

K – Kingella species

Because of taxonomic changes, many organisms historically placed under the “H” component are now classified as Aggregatibacter.

HACEK Endocarditis

The characteristic pattern is:

Oropharyngeal flora

• ●

Bacteremia

• ●

Cardiac valve infection

→ Consider a HACEK organism

Endocarditis may have a relatively indolent or subacute presentation.

Meningitis

Non-influenzae Haemophilus species can rarely cause meningitis.

Diagnosis requires appropriate examination and culture or molecular evaluation of cerebrospinal fluid.

Brain Abscess

Rare cases of brain abscess have also been associated with these organisms.

Because many originate from the oral or upper respiratory flora, CNS infection may occasionally follow contiguous spread or hematogenous dissemination.

Urinary Tract Infection

Although uncommon, some Haemophilus species have been associated with urinary tract infection.

Because these organisms require specialized culture conditions, routine urine culture techniques may occasionally fail to detect them.

Haemophilus aegyptius

Conjunctivitis

H. aegyptius is classically associated with:

Acute conjunctivitis

Historically, the organism has also been called the Koch-Weeks bacillus in association with acute conjunctival disease.

Brazilian Purpuric Fever

An especially important historical association is:

H. aegyptius → Brazilian purpuric fever

This is a severe systemic illness described particularly in children and characterized by:

• Acute fever

• Sepsis

• Purpuric skin lesions

• Rapid clinical deterioration

It was associated with particular invasive strains related to H. aegyptius.

High-Yield H. aegyptius Pattern

Child

• ●

Recent conjunctivitis

• ●

Acute fever and sepsis

• ●

Purpuric lesions

→ Think Brazilian purpuric fever associated with H. aegyptius

Diagnosis

The source lists:

Culture

as the primary diagnostic method.

Because these organisms are fastidious, appropriate media and incubation conditions are important.

For invasive disease, specimens may include:

• Blood

• Cerebrospinal fluid

• Respiratory specimens

• Abscess material

• Conjunctival specimens

Treatment

The source lists:

Ampicillin

as a treatment option.

For endocarditis or severe sepsis, the older source describes combining ampicillin with an:

Aminoglycoside

However, treatment of serious infection should account for modern susceptibility patterns and the specific organism identified.

Additional Treatment

The source lists:

• Third-generation cephalosporins

• Imipenem

• Meropenem

For invasive disease, antimicrobial selection should be guided by species identification, susceptibility testing, infection site, and severity.

High-Yield Clinical Pattern – Endocarditis

Fastidious Gram-negative coccobacillus

• ●

Normal oral/oropharyngeal flora

• ●

Subacute endocarditis

→ Consider a HACEK organism, including organisms historically classified among Haemophilus species.

Species Associations

H. aegyptius

→ Conjunctivitis

→ Brazilian purpuric fever

H. parainfluenzae

→ Respiratory infection

→ Occasionally bacteremia/endocarditis

Former H. aphrophilus / H. paraphrophilus

→ Now Aggregatibacter aphrophilus

→ Particularly important in invasive disease, including endocarditis and brain abscess

Former H. segnis

→ Now Aggregatibacter segnis

Exam Essentials

Genus: Haemophilus

Morphology: Gram-negative coccobacilli

Distribution: Worldwide

Typical habitat: Oral and upper respiratory flora

Major infections: Bacteremia, respiratory infection, pneumonia, endocarditis

Other infections: Meningitis, brain abscess, UTI, soft-tissue infection

Important species: H. aegyptius

H. aegyptius infection: Conjunctivitis

Severe H. aegyptius association: Brazilian purpuric fever

Purpuric fever pattern: Conjunctivitis followed by fever, sepsis, and purpura

Endocarditis association: HACEK organisms

Taxonomic change: H. aphrophilus → Aggregatibacter aphrophilus

Diagnosis: Culture

Treatment in source: Ampicillin

Additional treatment: Third-generation cephalosporin or carbapenem

Modern principle: Species identification and susceptibility-guided therapy

Key clinical pearl: Non-influenzae Haemophilus species are uncommon but important causes of invasive infection. Remember two particularly high-yield associations: fastidious oral Gram-negative organisms with endocarditis → think HACEK, and H. aegyptius with conjunctivitis followed by fulminant sepsis and purpura → Brazilian purpuric fever.

Infectious Disease and Microbiology – Haemophilus Species

Overview

Non-influenzae Haemophilus species are small, fastidious Gram-negative coccobacilli that occur worldwide. Many colonize the upper respiratory and oral mucosa, but they can occasionally cause invasive disease, particularly bacteremia, endocarditis, pneumonia, meningitis, brain abscess, and soft-tissue infection.

Certain species have especially important clinical associations. Haemophilus aegyptius is associated with conjunctivitis and historically with a severe purpuric septic syndrome, while some species formerly classified as Haemophilus are important causes of HACEK endocarditis.

Important Species

The source lists:

• Haemophilus aegyptius

• Haemophilus aphrophilus

• Haemophilus haemolyticus

• Haemophilus parahaemolyticus

• Haemophilus parainfluenzae

• Haemophilus paraphrophilus

• Haemophilus segnis

Several of these organisms have undergone taxonomic reclassification.

Important Taxonomic Changes

Older microbiology references may use Haemophilus names that are no longer preferred.

Notably:

Haemophilus aphrophilus → Aggregatibacter aphrophilus

Haemophilus paraphrophilus → now included within Aggregatibacter aphrophilus

Haemophilus segnis → Aggregatibacter segnis

These changes are particularly important when studying HACEK organisms and infective endocarditis.

Microbiologic Characteristics

Haemophilus species are generally:

• Gram-negative coccobacilli

• Fastidious organisms

• Facultatively anaerobic, although older sources may describe them as aerobic

• Associated with human mucosal surfaces

Different species have different requirements for X factor (hemin) and V factor (NAD), which can assist laboratory identification.

Epidemiology

These organisms have a worldwide distribution.

Many species colonize the:

• Oropharynx

• Upper respiratory tract

• Oral cavity

Infection frequently develops when organisms invade beyond their normal mucosal habitat.

Bacteremia

Non-influenzae Haemophilus species can occasionally cause bacteremia.

Bloodstream infection may occur:

• With endocarditis

• During severe respiratory infection

• In immunocompromised patients

• As part of systemic sepsis

Persistent bacteremia should raise concern for an endovascular focus such as infective endocarditis.

Upper Respiratory Tract Infection

Some Haemophilus species can cause or participate in:

• Pharyngitis

• Other upper respiratory infections

• Respiratory tract colonization with subsequent invasive disease

Because several species may colonize the respiratory tract, culture results should be interpreted together with the clinical syndrome.

Epiglottitis

Although H. influenzae type b is the classic Haemophilus associated with epiglottitis, other Haemophilus species have occasionally been implicated.

Epiglottitis remains an airway emergency because rapidly progressive swelling can cause upper-airway obstruction.

Pneumonia and Chronic Bronchitis

These organisms may cause:

• Pneumonia

• Exacerbations of chronic bronchitis

• Other lower respiratory tract infections

Respiratory disease is particularly relevant in patients with underlying pulmonary abnormalities.

Soft-Tissue Infection

Rare soft-tissue infections may occur when organisms gain access through disrupted mucosal or skin barriers.

Deep specimens are generally more useful than superficial cultures for determining whether an isolate represents true infection.

Endocarditis

Important Clinical Association

Some organisms historically classified as Haemophilus are particularly important causes of infective endocarditis.

This includes organisms now classified within Aggregatibacter.

These organisms belong to the clinically important HACEK group.

HACEK Organisms

HACEK refers to a group of fastidious Gram-negative organisms associated particularly with infective endocarditis:

H – Haemophilus species traditionally included in the group

A – Aggregatibacter species

C – Cardiobacterium hominis

E – Eikenella corrodens

K – Kingella species

Because of taxonomic changes, many organisms historically placed under the “H” component are now classified as Aggregatibacter.

HACEK Endocarditis

The characteristic pattern is:

Oropharyngeal flora

• ●

Bacteremia

• ●

Cardiac valve infection

→ Consider a HACEK organism

Endocarditis may have a relatively indolent or subacute presentation.

Meningitis

Non-influenzae Haemophilus species can rarely cause meningitis.

Diagnosis requires appropriate examination and culture or molecular evaluation of cerebrospinal fluid.

Brain Abscess

Rare cases of brain abscess have also been associated with these organisms.

Because many originate from the oral or upper respiratory flora, CNS infection may occasionally follow contiguous spread or hematogenous dissemination.

Urinary Tract Infection

Although uncommon, some Haemophilus species have been associated with urinary tract infection.

Because these organisms require specialized culture conditions, routine urine culture techniques may occasionally fail to detect them.

Haemophilus aegyptius

Conjunctivitis

H. aegyptius is classically associated with:

Acute conjunctivitis

Historically, the organism has also been called the Koch-Weeks bacillus in association with acute conjunctival disease.

Brazilian Purpuric Fever

An especially important historical association is:

H. aegyptius → Brazilian purpuric fever

This is a severe systemic illness described particularly in children and characterized by:

• Acute fever

• Sepsis

• Purpuric skin lesions

• Rapid clinical deterioration

It was associated with particular invasive strains related to H. aegyptius.

High-Yield H. aegyptius Pattern

Child

• ●

Recent conjunctivitis

• ●

Acute fever and sepsis

• ●

Purpuric lesions

→ Think Brazilian purpuric fever associated with H. aegyptius

Diagnosis

The source lists:

Culture

as the primary diagnostic method.

Because these organisms are fastidious, appropriate media and incubation conditions are important.

For invasive disease, specimens may include:

• Blood

• Cerebrospinal fluid

• Respiratory specimens

• Abscess material

• Conjunctival specimens

Treatment

The source lists:

Ampicillin

as a treatment option.

For endocarditis or severe sepsis, the older source describes combining ampicillin with an:

Aminoglycoside

However, treatment of serious infection should account for modern susceptibility patterns and the specific organism identified.

Additional Treatment

The source lists:

• Third-generation cephalosporins

• Imipenem

• Meropenem

For invasive disease, antimicrobial selection should be guided by species identification, susceptibility testing, infection site, and severity.

High-Yield Clinical Pattern – Endocarditis

Fastidious Gram-negative coccobacillus

• ●

Normal oral/oropharyngeal flora

• ●

Subacute endocarditis

→ Consider a HACEK organism, including organisms historically classified among Haemophilus species.

Species Associations

H. aegyptius

→ Conjunctivitis

→ Brazilian purpuric fever

H. parainfluenzae

→ Respiratory infection

→ Occasionally bacteremia/endocarditis

Former H. aphrophilus / H. paraphrophilus

→ Now Aggregatibacter aphrophilus

→ Particularly important in invasive disease, including endocarditis and brain abscess

Former H. segnis

→ Now Aggregatibacter segnis

Exam Essentials

Genus: Haemophilus

Morphology: Gram-negative coccobacilli

Distribution: Worldwide

Typical habitat: Oral and upper respiratory flora

Major infections: Bacteremia, respiratory infection, pneumonia, endocarditis

Other infections: Meningitis, brain abscess, UTI, soft-tissue infection

Important species: H. aegyptius

H. aegyptius infection: Conjunctivitis

Severe H. aegyptius association: Brazilian purpuric fever

Purpuric fever pattern: Conjunctivitis followed by fever, sepsis, and purpura

Endocarditis association: HACEK organisms

Taxonomic change: H. aphrophilus → Aggregatibacter aphrophilus

Diagnosis: Culture

Treatment in source: Ampicillin

Additional treatment: Third-generation cephalosporin or carbapenem

Modern principle: Species identification and susceptibility-guided therapy

Key clinical pearl: Non-influenzae Haemophilus species are uncommon but important causes of invasive infection. Remember two particularly high-yield associations: fastidious oral Gram-negative organisms with endocarditis → think HACEK, and H. aegyptius with conjunctivitis followed by fulminant sepsis and purpura → Brazilian purpuric fever.

Infectious Disease and Microbiology – Haemophilus influenzae

Overview

Haemophilus influenzae is a small Gram-negative coccobacillus that can cause both invasive and mucosal disease. Clinically, it is useful to distinguish encapsulated strains, especially serotype b (Hib), from nonencapsulated or nontypeable strains.

Before widespread Hib vaccination, H. influenzae type b was a major cause of meningitis, epiglottitis, bacteremia, cellulitis, and septic arthritis in children. Vaccination has dramatically reduced these invasive childhood infections.

Microbiologic Characteristics

H. influenzae is:

• A small Gram-negative coccobacillus

• Facultatively anaerobic

• Fastidious in culture

• Capable of existing as encapsulated or nonencapsulated strains

A classic laboratory feature is its requirement for:

Factor X = hemin

and

Factor V = NAD

for growth.

Culture Characteristics

H. influenzae grows well on:

Chocolate agar

because heating of blood releases the required X and V factors.

It may also demonstrate the satellitism phenomenon when growing near organisms such as Staphylococcus aureus, which supply growth factors.

Incubation Period

For invasive disease such as meningitis, the incubation period is not precisely established, but the source supports approximately:

2–4 days

Epidemiology

H. influenzae occurs worldwide.

The epidemiology changed markedly after introduction of conjugate vaccines against Hib.

Routine Hib immunization has produced a dramatic reduction in invasive serotype b disease in vaccinated populations.

Encapsulated H. influenzae Type b

Importance of the Capsule

The polysaccharide capsule, particularly the serotype b capsule, is a major virulence factor.

Hib can invade the bloodstream and disseminate to normally sterile sites, causing severe disease especially in young children.

Invasive Hib Disease in Children

Classically, Hib causes:

• Meningitis

• Epiglottitis

• Cellulitis

• Septic arthritis

• Bacteremia

These infections are often associated with bloodstream invasion.

Hib Meningitis

Before widespread vaccination, Hib was one of the major causes of bacterial meningitis in young children.

Clinical manifestations may include:

• Fever

• Irritability

• Lethargy

• Vomiting

• Neck stiffness

• Altered mental status

• Seizures in severe disease

This presentation is now much less common in appropriately vaccinated populations.

Epiglottitis

Hib is classically associated with acute epiglottitis, particularly in unvaccinated children.

Typical findings include:

• Abrupt fever

• Severe sore throat

• Dysphagia

• Drooling

• Muffled voice

• Inspiratory stridor

• Respiratory distress

A child may sit in a tripod position to maximize airway patency.

Epiglottitis – Airway Emergency

The major danger of epiglottitis is:

Rapid upper-airway obstruction

Therefore, airway management takes priority over attempts to directly examine the throat in a patient with severe suspected epiglottitis.

Nontypeable H. influenzae

Overview

Nonencapsulated strains, commonly called nontypeable H. influenzae (NTHi), more often cause localized mucosal respiratory infections.

These infections are particularly common in older children and adults.

Otitis Media

Nontypeable H. influenzae is an important cause of:

Acute otitis media

especially in children.

Sinusitis

Nontypeable strains also commonly contribute to:

Acute bacterial sinusitis

often alongside organisms such as Streptococcus pneumoniae and Moraxella catarrhalis.

Chronic Bronchitis and COPD Exacerbation

In adults, particularly those with chronic airway disease, nontypeable H. influenzae may cause:

• Acute exacerbations of chronic bronchitis

• COPD exacerbations

• Lower respiratory tract infection

Pneumonia

H. influenzae may cause pneumonia, particularly in:

• Older adults

• Patients with chronic lung disease

• Immunocompromised individuals

Nontypeable strains are particularly important in adult respiratory infections.

Bacteremia

Although invasive bloodstream infection is classically associated with encapsulated strains, bacteremia can occasionally occur with nonencapsulated strains as well.

Severe Infection in Asplenic Patients

Patients with absent or impaired splenic function are at increased risk for severe infections from encapsulated organisms.

Thus, H. influenzae can produce:

Rapidly progressive sepsis

in patients with:

• Anatomic asplenia

• Functional asplenia

The clinical course can be fulminant.

Epididymitis and Orchitis

The source also lists:

• Epididymitis

• Orchitis

as uncommon manifestations of H. influenzae infection.

Diagnosis

The source describes antigen detection methods including:

• Coagglutination

• Counterimmunoelectrophoresis

• Latex agglutination

These techniques can detect bacterial antigen in secretions or sterile body fluids.

Modern Diagnostic Approach

Depending on the clinical syndrome, diagnosis may also include:

• Culture

• Blood cultures

• CSF culture

• Respiratory specimen culture

• PCR or other molecular testing

For invasive disease, culture and molecular methods are generally more informative than older antigen-detection techniques alone.

Treatment

The source lists:

Amoxicillin–clavulanate

or

Second- or third-generation cephalosporins

as treatment options.

Selection depends on the site and severity of infection.

Invasive Disease

For serious invasive infections such as meningitis, a third-generation cephalosporin, such as ceftriaxone or cefotaxime, is typically an important therapeutic choice.

β-lactamase production and other resistance mechanisms can make plain ampicillin or amoxicillin unreliable without susceptibility information.

Additional Treatment

The source lists:

• Trimethoprim–sulfamethoxazole

• Fluoroquinolones

• Azithromycin

• Aztreonam

• Imipenem

• Meropenem

Choice should be guided by the infection site, severity, patient factors, and susceptibility results.

β-Lactamase Production

Some H. influenzae strains produce β-lactamase, resulting in resistance to ampicillin and amoxicillin.

Therefore:

Amoxicillin alone may fail

whereas:

Amoxicillin–clavulanate

can overcome many β-lactamase-producing strains.

Prevention

Hib Conjugate Vaccine

The most important preventive measure is:

Hib conjugate vaccination

The vaccine contains capsular polysaccharide linked to a protein carrier, allowing an effective immune response in young children.

It is highly effective and has dramatically reduced invasive Hib disease.

Age for Vaccination

The source notes effective vaccination in children older than:

2 months

which corresponds to the age at which routine infant Hib immunization programs begin in many countries.

Postexposure Prophylaxis

Close contacts of a patient with invasive Hib disease may require antimicrobial prophylaxis under appropriate public-health circumstances.

The classic drug is:

Rifampin

The source also mentions ciprofloxacin as a protective measure.

Who May Need Prophylaxis?

Postexposure prophylaxis is particularly considered for selected:

• Household contacts

• Childcare contacts

• Individuals in environments containing incompletely vaccinated or vulnerable young children

Public-health recommendations should guide who receives prophylaxis.

High-Yield Clinical Pattern – Hib

Unvaccinated young child

• ●

Fever

• ●

Meningitis, epiglottitis, cellulitis, or septic arthritis

• ●

Bacteremia

→ Think Haemophilus influenzae type b

High-Yield Clinical Pattern – Nontypeable H. influenzae

Adult with chronic lung disease

• ●

COPD/chronic bronchitis exacerbation

or

Child with otitis media or sinusitis

→ Think nontypeable H. influenzae

Classic Laboratory Pattern

Small Gram-negative coccobacillus

• ●

Requires factor X and factor V

• ●

Grows on chocolate agar

→ Think Haemophilus influenzae

Hib vs. Nontypeable H. influenzae

Hib:

Encapsulated → invasive disease → meningitis, epiglottitis, bacteremia, septic arthritis

Nontypeable strains:

No capsule → mucosal respiratory disease → otitis, sinusitis, bronchitis/COPD exacerbation, pneumonia

Exam Essentials

Organism: Haemophilus influenzae

Type: Gram-negative coccobacillus

Growth requirements: Factors X and V

Culture medium: Chocolate agar

Major virulence factor of Hib: Polysaccharide capsule

Important serotype: Type b

Incubation for invasive disease: Approximately 2–4 days

Hib infections: Meningitis, epiglottitis, bacteremia, cellulitis, septic arthritis

Nontypeable infections: Otitis media, sinusitis, bronchitis/COPD exacerbation, pneumonia

High-risk group for fulminant sepsis: Asplenic patients

Diagnosis: Culture, molecular testing; antigen detection historically used

Treatment: Amoxicillin–clavulanate for appropriate mucosal disease; third-generation cephalosporins for serious invasive disease

Resistance mechanism: β-lactamase production

Prevention: Hib conjugate vaccine

Postexposure prophylaxis: Rifampin for selected close contacts

Key clinical pearl: Haemophilus influenzae type b is an encapsulated invasive pathogen classically associated with meningitis and epiglottitis in unvaccinated children, whereas nontypeable strains primarily cause otitis media, sinusitis, COPD exacerbations, and pneumonia. The organism requires factors X and V and classically grows on chocolate agar.

Infectious Disease and Microbiology – Haemophilus ducreyi

Overview

Haemophilus ducreyi is an aerobic Gram-negative coccobacillus that causes chancroid, a sexually transmitted infection characterized by painful genital ulcers with tender inguinal lymphadenopathy.

The disease is more common in tropical and subtropical regions, although outbreaks have also occurred in the United States.

Microbiologic Characteristics

Haemophilus ducreyi is:

• A Gram-negative coccobacillus

• Aerobic

• Fastidious and relatively difficult to culture

• The causative organism of chancroid

Its fastidious growth requirements explain why culture requires special media.

Incubation Period

The incubation period is usually:

3–5 days

but may occasionally extend to:

Up to 2 weeks

Symptoms typically begin with a papule that progresses to a painful ulcer.

Epidemiology

Chancroid is more common in:

• Tropical regions

• Subtropical regions

• Areas with limited access to sexually transmitted infection control services

Historically, outbreaks have occurred in the United States, including among inner-city populations and migrant agricultural workers.

The source notes that men are more commonly affected.

Transmission

H. ducreyi is transmitted primarily through:

Sexual contact

Infection occurs when the organism gains access through small breaks in genital or perigenital skin and mucosa.

Chancroid

The classic infection is:

Chancroid

This is a genital ulcerative disease characterized by:

• Painful genital ulceration

• Tender regional lymphadenopathy

• Possible suppurative inguinal lymph nodes

The ulcer is typically more painful and inflammatory than the chancre of primary syphilis.

Genital Ulcer

A typical chancroid ulcer is:

• Painful

• Soft rather than indurated

• Irregular in shape

• Surrounded by inflammation

• Often associated with purulent or necrotic material

This appearance contrasts with the typically painless ulcer of primary syphilis.

Inguinal Adenopathy

Tender inguinal lymphadenopathy is a characteristic feature.

Affected lymph nodes may:

• Become enlarged

• Be painful

• Become fluctuant

• Suppurate

A fluctuant suppurative lymph node is often called a:

Bubo

Chancroid vs. Syphilis

Chancroid –

H. ducreyi

Painful ulcer

• ●

Tender inguinal lymphadenopathy

• ●

Soft, irregular ulcer

Primary Syphilis –

Treponema pallidum

Usually painless chancre

• ●

Typically nontender lymphadenopathy

This distinction is highly useful clinically and for examinations.

Chancroid vs. Genital Herpes

Both chancroid and genital herpes can cause painful genital ulcers.

However:

Chancroid

→ Often a deeper, irregular ulcer with purulent base and tender adenopathy

Genital herpes

→ Often begins with clusters of painful vesicles that ulcerate

Laboratory testing is important when the diagnosis is uncertain.

Diagnosis

The source lists:

Culture using special media

Because H. ducreyi is fastidious, culture can be technically difficult and may have limited sensitivity.

Diagnosis therefore often depends on clinical findings combined with exclusion or testing for other causes of genital ulcer disease.

Differential Diagnosis of Genital Ulcers

Important causes include:

• Haemophilus ducreyi → chancroid

• Treponema pallidum → syphilis

• Herpes simplex virus → genital herpes

• Chlamydia trachomatis L1–L3 → lymphogranuloma venereum

• Klebsiella granulomatis → granuloma inguinale

Treatment

The source lists:

Ceftriaxone 250 mg IM as a single dose

or

Azithromycin 1 g as a single dose

or

Ciprofloxacin 500 mg orally every 12 hours for 3 days

These are classic treatment regimens for chancroid.

Additional Treatment

Additional treatments listed in the source include:

• Erythromycin

• Trimethoprim–sulfamethoxazole

• Ofloxacin

Choice of therapy should take into account current recommendations, local susceptibility patterns, pregnancy status, and drug interactions.

Management of Fluctuant Inguinal Nodes

If inguinal adenopathy becomes:

Fluctuant

and especially if it is large,

the source recommends:

Needle aspiration

Drainage can relieve discomfort and reduce the risk of spontaneous rupture.

Prevention

General prevention includes:

Safe-sex practices

This includes:

• Consistent barrier protection

• Reduction of high-risk sexual exposure

• Evaluation and treatment of sexual partners when appropriate

• Testing for other sexually transmitted infections

Important STI Association

Patients with chancroid should also be evaluated for other sexually transmitted infections because genital ulcers can increase the risk of acquisition and transmission of infections such as HIV.

High-Yield Clinical Pattern

Recent sexual exposure

• ●

Incubation of about 3–5 days

• ●

Painful genital ulcer

• ●

Tender inguinal lymphadenopathy or bubo

→ Think Haemophilus ducreyi causing chancroid

Exam Essentials

Organism: Haemophilus ducreyi

Type: Gram-negative coccobacillus

Major disease: Chancroid

Transmission: Sexual contact

Incubation: Usually 3–5 days

Geography: More common in tropical and subtropical regions

Genital ulcer: Painful, soft, irregular

Lymph nodes: Tender inguinal adenopathy, sometimes fluctuant

Suppurative node: Bubo

Diagnosis in source: Culture on special media

Treatment in source: Ceftriaxone, azithromycin, or ciprofloxacin

Large fluctuant node: Needle aspiration

Prevention: Safe-sex practices

Classic distinction: Chancroid is painful; primary syphilis is usually painless

Key clinical pearl: Haemophilus ducreyi causes chancroid, classically presenting as a painful soft genital ulcer with tender inguinal lymphadenopathy or buboes. The painful ulcer is the major clue distinguishing chancroid from the typically painless chancre of primary syphilis.

Infectious Disease and Microbiology – Gnathostoma spinigerum

Overview

Gnathostoma spinigerum is a parasitic nematode (roundworm) that normally infects dogs and cats. Humans are accidental hosts and develop gnathostomiasis after ingesting infective larvae, classically in raw or undercooked fish or other intermediate/paratenic hosts.

A characteristic manifestation is intermittent migratory, pruritic subcutaneous swelling accompanied by peripheral eosinophilia. Larval migration into the central nervous system or eye can produce severe neurologic or ocular disease.

Microbiologic Characteristics

Gnathostoma spinigerum is:

• A nematode helminth

• Primarily a parasite of dogs and cats

• Acquired by humans through ingestion of infective larvae

• Characterized in humans by tissue migration of larvae

Humans are generally accidental hosts in whom the parasite does not complete its normal life cycle.

Epidemiology

Gnathostomiasis is particularly associated with:

• Thailand

• Japan

• China

• Other parts of Southeast Asia

The source notes that many reported cases have historically come from Thailand.

Transmission

Human infection is most commonly acquired through ingestion of raw or inadequately cooked food containing infective larvae.

Important exposures include:

• Raw or undercooked freshwater fish

• Poultry and other potential paratenic hosts

Thus, dietary history can provide an important diagnostic clue.

Life Cycle in Humans

After infective larvae are swallowed:

Ingestion of larvae

→

Penetration of the gastrointestinal tract

→

Migration through tissues

→

Inflammatory and eosinophilic response

Because humans are accidental hosts, larvae may continue migrating rather than developing normally into mature adult worms.

Gnathostomiasis

The disease caused by Gnathostoma is called:

Gnathostomiasis

The characteristic clinical feature is migratory tissue disease caused by movement of larvae through different parts of the body.

Cutaneous Gnathostomiasis

The classic presentation consists of:

Transient, migratory, pruritic erythematous swelling

The lesions may:

• Appear suddenly

• Be intensely pruritic

• Become erythematous and edematous

• Disappear and recur elsewhere

• Reflect migration of the larva through subcutaneous tissues

This recurrent migratory pattern is highly suggestive in an appropriate epidemiologic setting.

Eosinophilia

Peripheral eosinophilia is an important laboratory finding.

The combination of:

Migratory subcutaneous swelling

• ●

Eosinophilia

• ●

History of raw or undercooked fish consumption in an endemic region

should strongly suggest gnathostomiasis.

Neurologic Gnathostomiasis

Larvae may migrate into the central nervous system, producing potentially serious neurologic disease.

Manifestations can include:

• Focal cerebral lesions

• Meningitic or meningoencephalitic manifestations

• Radicular symptoms

• Other focal neurologic abnormalities

Neurologic involvement is one of the most serious complications.

Cerebrospinal Fluid Findings

An important clue in CNS gnathostomiasis is:

Eosinophilic pleocytosis of the CSF

Therefore:

Neurologic symptoms + CSF eosinophilia + compatible dietary/travel exposure

→ Consider a tissue-invasive helminth such as Gnathostoma spinigerum.

Eosinophilic Meningitis

Because larvae can invade the nervous system, gnathostomiasis is an important parasitic cause of eosinophilic meningitis or meningoencephalitis.

The differential diagnosis of eosinophilic meningitis also includes other helminthic infections, particularly Angiostrongylus cantonensis.

Ocular Gnathostomiasis

Larvae may occasionally migrate into the eye.

Ocular infection can cause:

• Ocular inflammation

• Visual disturbances

• Pain

• Visible or migrating intraocular parasite

When technically possible, removal of the parasite may be both diagnostic and therapeutic.

Diagnosis

The source describes definitive diagnosis by:

Extraction and identification of the parasite

Demonstration of the actual larva provides direct confirmation of infection.

Clinical Diagnosis

Because recovery of the parasite is not always possible, suspicion may arise from the combination of:

Compatible exposure

• ●

Migratory cutaneous lesions

• ●

Peripheral eosinophilia

or

Neurologic disease with CSF eosinophilia

The epidemiologic history is therefore particularly important.

Treatment

The source notes that the effectiveness of antihelminthic therapy was historically uncertain but that treatment was commonly administered.

It lists:

Albendazole 400 mg orally every 12 hours for 14 days

as a treatment regimen.

Additional Treatment

The source reports successful treatment of ocular disease using:

Mebendazole

However, when an accessible worm is present—particularly in ocular or superficial disease—physical extraction of the parasite may play an important role.

Prevention

Prevention primarily involves avoiding ingestion of viable larvae.

Important measures include:

• Thoroughly cooking freshwater fish

• Avoiding raw or inadequately cooked potential intermediate/paratenic hosts

• Following safe food-preparation practices in endemic regions

High-Yield Clinical Pattern

Travel/residence in Southeast Asia

• ●

Raw or undercooked freshwater fish exposure

• ●

Recurrent migratory pruritic subcutaneous swelling

• ●

Peripheral eosinophilia

→ Think Gnathostoma spinigerum

Neurologic High-Yield Pattern

Compatible food exposure

• ●

Neurologic symptoms

• ●

Focal CNS abnormalities

• ●

Eosinophilic pleocytosis in CSF

→ Consider neurognathostomiasis

Exam Essentials

Organism: Gnathostoma spinigerum

Type: Nematode helminth

Natural definitive hosts: Dogs and cats

Human role: Accidental host

Major geographic association: Southeast Asia, particularly Thailand

Transmission: Ingestion of infective larvae in raw/undercooked food, classically freshwater fish

Pathogenesis: Larval tissue migration

Classic manifestation: Migratory pruritic erythematous subcutaneous swelling

Major laboratory clue: Eosinophilia

CNS complication: Neurognathostomiasis

CSF finding: Eosinophilic pleocytosis

Ocular disease: Possible through larval migration

Definitive diagnosis: Extraction and identification of parasite

Treatment in source: Albendazole 400 mg q12h for 14 days

Additional historical therapy: Mebendazole for ocular disease

Prevention: Avoid raw or undercooked potential intermediate/paratenic hosts

Key clinical pearl: Gnathostoma spinigerum should be strongly suspected when a patient with raw freshwater fish exposure in Southeast Asia develops recurrent migratory pruritic subcutaneous swellings with eosinophilia. CNS migration can cause eosinophilic meningitis or focal neurologic disease.

Infectious Disease and Microbiology – Geotrichum candidum

Overview

Geotrichum candidum is a filamentous fungus with septate hyphae that can produce arthroconidia in infected tissue. Human infection, sometimes referred to as geotrichosis, is rare but occurs worldwide.

The most important severe manifestation is disseminated infection in profoundly immunocompromised patients, particularly those with neutropenia.

Microbiologic Characteristics

Geotrichum candidum is characterized by:

• Filamentous fungal growth

• Septate hyphae

• Hyaline rather than pigmented hyphae

• Formation of arthroconidia (arthrospores)

In tissue, the characteristic appearance is:

Septate hyaline hyphae + arthroconidia

Arthroconidia

Arthroconidia are produced by fragmentation of fungal hyphae into individual rectangular or barrel-shaped cells.

Recognition of arthroconidia can provide an important clue to the identity of an arthroconidial fungus.

However, this morphology is not unique to Geotrichum, so culture and definitive organism identification remain important.

Epidemiology

Human infection is:

Rare

but has been reported worldwide.

Geotrichum organisms can be encountered in the environment, and colonization of human mucosal surfaces may occur without invasive disease.

Therefore, isolation of the organism does not automatically prove invasive infection.

Risk Factors

The most important risk factor for severe invasive disease is:

Profound neutropenia

Other states of significant immunosuppression may also increase the risk of invasive fungal disease.

Disseminated Geotrichosis

The major invasive manifestation described in the source is:

Disseminated disease in neutropenic patients

Once invasive infection develops, organisms may spread hematogenously and involve multiple organs.

This is a serious opportunistic fungal infection.

Clinical Pattern

The typical high-risk setting is:

Severely immunocompromised patient

• ●

Prolonged neutropenia

• ●

Persistent systemic illness despite antibacterial therapy

• ●

Evidence of invasive fungal infection

→ Consider an opportunistic mold or yeast-like fungus, including Geotrichum candidum

Diagnosis

Diagnosis is based on:

Identification of the fungus in tissue biopsy

and

Fungal culture

Demonstration of fungal invasion within tissue is particularly valuable because Geotrichum may occasionally represent colonization rather than invasive disease.

Histopathology

Tissue examination may demonstrate:

Hyaline septate hyphae

with

Arthroconidia

This appearance should prompt consideration of an arthroconidial fungus.

Culture

Culture allows the organism to be isolated and identified.

Because several fungi can produce arthroconidia, accurate laboratory identification is important for distinguishing Geotrichum from other morphologically similar fungi.

Important Differential Diagnosis

Arthroconidia may also be encountered with other fungi, making differentiation important.

For example:

Geotrichum

→ Hyaline septate hyphae with arthroconidia

Coccidioides

→ Produces arthroconidia environmentally, but spherules containing endospores are the characteristic tissue form

Thus:

Arthroconidia seen in tissue

→ favors an organism such as Geotrichum rather than Coccidioides.

Treatment

The source emphasizes that there are limited clinical data regarding optimal antifungal therapy for G. candidum infection.

It describes:

Intravenous amphotericin B

as having been used with moderate success.

Treatment Considerations

Because invasive geotrichosis is uncommon, management should take into account:

• Severity and extent of infection

• Antifungal susceptibility when available

• Underlying immune status

• Degree and duration of neutropenia

• Potential need for source control

Treatment of invasive disease should be individualized.

Importance of Immune Recovery

As with many opportunistic mold infections, improvement in host immune function can be extremely important.

In neutropenic patients:

Antifungal therapy

• ●

Recovery from neutropenia

→ improves the likelihood of controlling invasive fungal infection.

Persistent profound neutropenia can make disseminated disease particularly difficult to treat.

High-Yield Clinical Pattern

Profoundly neutropenic patient

• ●

Disseminated fungal infection

• ●

Tissue biopsy showing septate hyaline hyphae with arthroconidia

→ Think Geotrichum candidum

Exam Essentials

Organism: Geotrichum candidum

Disease: Geotrichosis

Type: Filamentous fungus / mold-like fungus

Hyphae: Septate and hyaline

Characteristic structure: Arthroconidia

Distribution: Worldwide

Frequency: Rare

Major risk factor: Neutropenia

Major severe manifestation: Disseminated infection

Diagnosis: Tissue biopsy + fungal culture

Tissue morphology: Septate hyaline hyphae with arthroconidia

Treatment in source: IV amphotericin B

Evidence base: Limited

Important management factor: Recovery of immune function/neutrophils

Key clinical pearl: Geotrichum candidum is a rare opportunistic fungus characterized by septate hyaline hyphae and arthroconidia in tissue. The classic severe presentation is disseminated infection in a profoundly neutropenic patient.

Medicine – Benign Essential Tremor

Essential tremor is a common movement disorder characterised primarily by an action tremor, meaning the tremor appears during voluntary movement or while maintaining a posture against gravity. It is usually bilateral and most often affects the hands and forearms, but the head and voice may also be involved.

The older term “benign essential tremor” is still encountered, but essential tremor is preferred because the condition can sometimes cause significant functional disability.

1. Tremor with Movement

The tremor of essential tremor is typically an action or postural tremor.

It is most noticeable when the patient:

Holds the arms outstretched.

Writes.

Uses cutlery.

Drinks from a cup.

Performs other fine hand movements.

A classic resting tremor is not the dominant feature.

2. Difference from Parkinson Tremor

Essential tremor is easiest to distinguish from Parkinson disease by the timing of the tremor.

Essential tremor → tremor mainly with posture or movement.

Parkinson disease → tremor classically occurs at rest.

Parkinson tremor is also often initially asymmetric and accompanied by bradykinesia and rigidity, whereas essential tremor usually lacks these Parkinsonian features.

3. Distribution

The hands and arms are most commonly affected.

The tremor may also involve:

Head.

Voice.

Less commonly, other body regions may be involved.

Head tremor may appear as repeated “yes-yes” or “no-no” movements.

4. Bilateral Tremor

Essential tremor is typically bilateral, although one side may initially be more noticeable than the other.

This differs from Parkinson disease, which often begins clearly asymmetrically.

5. Inheritance

Essential tremor often has a strong familial component.

Many families show an autosomal dominant pattern of inheritance, although the genetics are heterogeneous and not every patient has an affected relative.

Therefore, a positive family history supports the diagnosis but is not required.

6. Effect of Stress

The tremor commonly becomes worse with:

Anxiety.

Emotional stress.

Fatigue.

Sleep deprivation.

Stimulants such as excess caffeine.

Patients may therefore notice substantial day-to-day variation in severity.

7. Effect of Alcohol

A characteristic historical feature is temporary improvement after a small amount of alcohol.

This can be a useful diagnostic clue.

However, alcohol should not be recommended as a treatment because of tolerance, dependence, rebound worsening, and other health risks.

8. Neurological Examination

In otherwise typical essential tremor, the remainder of the neurological examination is generally normal.

There should not be prominent:

Bradykinesia.

Rigidity.

Cerebellar signs.

Focal neurological deficits.

The presence of these findings suggests another diagnosis.

9. Diagnosis

Essential tremor is primarily a clinical diagnosis.

The history and examination should establish a persistent bilateral upper-limb action tremor and exclude more likely alternative causes.

Investigations are usually directed toward excluding secondary causes when the presentation is atypical.

10. Secondary Causes to Exclude

Other causes of tremor include:

Hyperthyroidism.

Drug-induced tremor.

Excess caffeine or stimulants.

Alcohol withdrawal.

Parkinson disease.

Cerebellar disorders.

Dystonic tremor.

Therefore, the diagnosis should not be made solely because the tremor improves with alcohol.

11. Propranolol

Propranolol, a non-selective beta-blocker, is a major first-line treatment when the tremor causes functional impairment.

It can reduce tremor amplitude and improve tasks such as writing, eating, and drinking.

The old statement that only about 30% respond is too restrictive; response rates vary, and many patients obtain at least partial benefit.

12. Primidone

Another important first-line treatment is primidone.

Primidone is an anticonvulsant that can significantly reduce essential tremor and is often used when propranolol is ineffective, contraindicated, or not tolerated.

Therefore, the main medications to remember are:

Propranolol.

Primidone.

13. When Propranolol May Be Unsuitable

Because propranolol blocks beta receptors, it may be unsuitable in some patients, particularly those with:

Asthma.

Marked bradycardia.

Certain conduction abnormalities.

Treatment therefore needs to be individualised.

14. Other Treatment Options

If first-line treatment is inadequate, specialist management may include other medications or procedural treatments.

For severe disabling medication-resistant tremor, options may include:

Deep brain stimulation.

Focused ultrasound thalamotomy in selected patients.

These are generally reserved for significant refractory disease.

15. Essential Tremor – Note Form

Type of tremor: action/postural tremor.

Rest tremor: not the classic dominant feature.

Distribution: mainly hands and arms; head and voice may also be affected.

Inheritance: often autosomal dominant.

Stress: worsens tremor.

Alcohol: may temporarily improve tremor but is not a recommended treatment.

Neurological examination: otherwise usually normal.

First-line treatment: propranolol or primidone when symptoms are functionally troublesome.

Key Clinical Pattern

Remember essential tremor as:

Bilateral action tremor + hands/head involvement + worse with stress + may improve transiently with alcohol.

The easiest distinction is:

Essential tremor → action/postural tremor.

Parkinson disease → resting tremor + bradykinesia + rigidity.

And the key treatment pair is:

Propranolol or primidone.

1. Tremor with Movement The tremor of essential tremor is typically an action or postural tremor. It is most noticeable when the patient: Holds the arms outstretched. Writes. Uses cutlery. Drinks from a cup. Performs other fine hand movements. A classic resting tremor is not the dominant feature. 

2. Difference from Parkinson Tremor Essential tremor is easiest to distinguish from Parkinson disease by the timing of the tremor. Essential tremor → tremor mainly with posture or movement. Parkinson disease → tremor classically occurs at rest. Parkinson tremor is also often initially asymmetric and accompanied by bradykinesia and rigidity, whereas essential tremor usually lacks these Parkinsonian features. 

3. Distribution The hands and arms are most commonly affected. The tremor may also involve: Head. Voice. Less commonly, other body regions may be involved. Head tremor may appear as repeated “yes-yes” or “no-no” movements. 

4. Bilateral Tremor Essential tremor is typically bilateral, although one side may initially be more noticeable than the other. This differs from Parkinson disease, which often begins clearly asymmetrically. 

5. Inheritance Essential tremor often has a strong familial component. Many families show an autosomal dominant pattern of inheritance, although the genetics are heterogeneous and not every patient has an affected relative. Therefore, a positive family history supports the diagnosis but is not required. 

6. Effect of Stress The tremor commonly becomes worse with: Anxiety. Emotional stress. Fatigue. Sleep deprivation. Stimulants such as excess caffeine. Patients may therefore notice substantial day-to-day variation in severity. 

7. Effect of Alcohol A characteristic historical feature is temporary improvement after a small amount of alcohol. This can be a useful diagnostic clue. However, alcohol should not be recommended as a treatment because of tolerance, dependence, rebound worsening, and other health risks. 

8. Neurological Examination In otherwise typical essential tremor, the remainder of the neurological examination is generally normal. There should not be prominent: Bradykinesia. Rigidity. Cerebellar signs. Focal neurological deficits. The presence of these findings suggests another diagnosis. 

9. Diagnosis Essential tremor is primarily a clinical diagnosis. The history and examination should establish a persistent bilateral upper-limb action tremor and exclude more likely alternative causes. Investigations are usually directed toward excluding secondary causes when the presentation is atypical. 

10. Secondary Causes to Exclude Other causes of tremor include: Hyperthyroidism. Drug-induced tremor. Excess caffeine or stimulants. Alcohol withdrawal. Parkinson disease. Cerebellar disorders. Dystonic tremor. Therefore, the diagnosis should not be made solely because the tremor improves with alcohol. 

11. Propranolol Propranolol, a non-selective beta-blocker, is a major first-line treatment when the tremor causes functional impairment. It can reduce tremor amplitude and improve tasks such as writing, eating, and drinking. The old statement that only about 30% respond is too restrictive; response rates vary, and many patients obtain at least partial benefit. 

12. Primidone Another important first-line treatment is primidone. Primidone is an anticonvulsant that can significantly reduce essential tremor and is often used when propranolol is ineffective, contraindicated, or not tolerated. Therefore, the main medications to remember are: Propranolol. Primidone. 

13. When Propranolol May Be Unsuitable Because propranolol blocks beta receptors, it may be unsuitable in some patients, particularly those with: Asthma. Marked bradycardia. Certain conduction abnormalities. Treatment therefore needs to be individualised. 

14. Other Treatment Options If first-line treatment is inadequate, specialist management may include other medications or procedural treatments. For severe disabling medication-resistant tremor, options may include: Deep brain stimulation. Focused ultrasound thalamotomy in selected patients. These are generally reserved for significant refractory disease. 

15. Essential Tremor – Note Form Type of tremor: action/postural tremor. 

Rest tremor: not the classic dominant feature. 

Distribution: mainly hands and arms; head and voice may also be affected. 

Inheritance: often autosomal dominant. 

Stress: worsens tremor. 

Alcohol: may temporarily improve tremor but is not a recommended treatment. 

Neurological examination: otherwise usually normal. 

First-line treatment: propranolol or primidone when symptoms are functionally troublesome. 

Key Clinical Pattern Remember essential tremor as: Bilateral action tremor + hands/head involvement + worse with stress + may improve transiently with alcohol. The easiest distinction is: Essential tremor → action/postural tremor. Parkinson disease → resting tremor + bradykinesia + rigidity. And the key treatment pair is: Propranolol or primidone.

Medicine – Huntington Disease

Huntington disease (HD) is a progressive autosomal dominant neurodegenerative disorder characterised by a combination of chorea, psychiatric disturbance, and progressive cognitive decline. Symptoms most commonly begin in adult life, often between about 30 and 50 years of age, although onset can occur earlier or later.

Because the disorder is autosomal dominant, an affected person usually has an affected parent, although the family history may occasionally appear negative because of early parental death, unrecognised disease, or a new mutation.

1. Inheritance

Huntington disease is inherited in an autosomal dominant pattern.

This means that an affected individual has a 50% chance of transmitting the pathogenic variant to each child, regardless of the child’s sex.

Both males and females can therefore be affected and can transmit the disease.

2. Genetic Defect

Huntington disease is caused by expansion of a CAG trinucleotide repeat in the HTT gene on chromosome 4.

The CAG sequence codes for glutamine, so the mutation produces an abnormally long polyglutamine tract in the huntingtin protein.

The abnormal protein ultimately causes progressive neuronal dysfunction and death.

3. Anticipation

Huntington disease demonstrates anticipation.

This means that the disease can present at an earlier age in successive generations when the CAG repeat expands further.

Anticipation is particularly associated with paternal transmission, because repeat expansion is more likely during spermatogenesis.

Therefore:

More CAG repeats → generally earlier disease onset.

4. Neuropathology

The most characteristic pathological changes involve degeneration of neurons within the striatum, especially the:

Caudate nucleus.

Putamen.

Loss of striatal neurons disrupts the normal basal-ganglia control of movement and contributes to chorea and other motor abnormalities.

5. Caudate Atrophy

As the disease progresses, marked caudate nucleus atrophy may develop.

On brain imaging this can produce enlargement of the frontal horns of the lateral ventricles.

This is a classic structural feature of advanced Huntington disease.

6. Age of Onset

Symptoms classically begin between approximately 30 and 50 years of age.

However, there is considerable variation.

Some patients develop disease later in life, while those with very large CAG expansions can present much earlier.

7. Juvenile Huntington Disease

Disease beginning before about 20 years of age is called juvenile Huntington disease.

Unlike classic adult Huntington disease, juvenile cases may show more:

Rigidity.

Bradykinesia.

Dystonia.

Seizures.

Chorea may actually be less prominent.

This juvenile phenotype is sometimes called the Westphal variant.

8. Chorea

Chorea is the characteristic movement disorder of classic Huntington disease.

It consists of involuntary, irregular, unpredictable, flowing movements that seem to move randomly from one part of the body to another.

The movements are not rhythmic.

They may affect the:

Face.

Arms.

Legs.

Trunk.

9. Appearance of Chorea

Early chorea may initially look like normal restlessness or fidgeting.

Patients may incorporate involuntary movements into apparently purposeful actions, sometimes making them difficult to recognise initially.

As disease progresses, the movements become more obvious and may interfere with walking, speech, eating, and daily activities.

10. Other Motor Features

Huntington disease is not limited to chorea.

Patients may also develop:

Dystonia.

Abnormal eye movements.

Dysarthria.

Dysphagia.

Impaired gait and balance.

In advanced disease, chorea may become less prominent while rigidity and bradykinesia increase.

11. Cognitive Decline

Progressive cognitive impairment is a central component of Huntington disease.

Early abnormalities commonly involve executive function, including difficulty with:

Planning.

Organisation.

Problem solving.

Attention.

Mental flexibility.

As the disease progresses, cognitive impairment may eventually develop into dementia.

12. Dementia

Dementia usually develops gradually as neurodegeneration progresses.

Unlike Alzheimer’s disease, early problems may be dominated by executive dysfunction and slowed thinking rather than severe early loss of episodic memory.

Eventually, multiple cognitive domains become affected.

13. Psychiatric Features

Psychiatric symptoms are extremely important and may precede the obvious movement disorder.

These can include:

Depression.

Irritability.

Anxiety.

Apathy.

Impulsivity.

Obsessive or compulsive behaviour.

Psychosis in some patients.

Therefore, Huntington disease should be considered a motor, cognitive, and psychiatric disorder.

14. Family History

A positive family history strongly supports the diagnosis because Huntington disease is autosomal dominant.

A typical history may reveal a parent or grandparent who developed unusual movements, personality changes, psychiatric illness, or progressive dementia during adulthood.

However, an apparently negative family history does not completely exclude the disease.

15. Genetic Testing

The diagnosis can be confirmed by molecular genetic testing demonstrating an expanded CAG repeat in the HTT gene.

Testing an individual who already has compatible symptoms is called diagnostic genetic testing.

16. Predictive Genetic Testing

Because Huntington disease usually develops in adulthood, an asymptomatic adult with an affected parent may request predictive testing.

This is a major decision because a positive result predicts a high likelihood of future disease before symptoms appear.

Predictive testing therefore requires careful genetic counselling, informed consent, and psychological support.

17. Treatment Principles

There is currently no treatment that reliably reverses the underlying neurodegeneration.

Management therefore focuses on:

Controlling abnormal movements.

Treating psychiatric symptoms.

Maintaining nutrition and swallowing safety.

Physiotherapy and mobility support.

Speech and language therapy.

Genetic counselling.

Psychological and social support.

18. Treatment of Chorea

The older note lists chlorpromazine to relieve chorea.

Dopamine-blocking antipsychotic drugs can indeed reduce choreiform movements, particularly when the patient also has behavioural disturbance or psychosis.

However, chlorpromazine is not generally regarded as the principal modern treatment specifically for Huntington chorea.

19. Tetrabenazine

Tetrabenazine is an important treatment for troublesome Huntington-related chorea.

It inhibits vesicular monoamine transporter type 2 (VMAT2), reducing storage and release of monoamines such as dopamine.

The resulting reduction in dopaminergic activity helps suppress choreiform movements.

20. Deutetrabenazine

Deutetrabenazine is a related VMAT2 inhibitor that may also be used to treat Huntington chorea.

Drug selection depends on availability, individual symptoms, adverse-effect risk, and specialist assessment.

21. Antipsychotic Drugs

Antipsychotic drugs may be especially useful when chorea occurs together with:

Psychosis.

Severe agitation.

Aggressive behaviour.

Some atypical antipsychotics are often preferred over older drugs such as chlorpromazine because treatment can be tailored according to adverse effects and psychiatric symptoms.

22. Depression and Suicide Risk

Depression is common in Huntington disease and requires active treatment.

Patients can also have an increased risk of suicidal thoughts and behaviour, particularly around diagnosis and during periods of declining function.

Psychiatric assessment and ongoing support are therefore essential components of care.

23. Dysphagia and Nutrition

Progressive motor dysfunction may cause dysphagia.

At the same time, continuous involuntary movements can increase energy expenditure.

Patients may consequently develop significant weight loss and nutritional problems.

Swallowing assessment and nutritional support become increasingly important as disease advances.

24. Huntington Disease – Note Form

Inheritance: autosomal dominant.

Gene: HTT gene on chromosome 4.

Mutation: CAG trinucleotide repeat expansion.

Anticipation: increasing CAG repeat length can cause earlier onset in later generations, particularly with paternal transmission.

Typical onset: approximately 30–50 years, although highly variable.

Main movement disorder: chorea.

Chorea: irregular, involuntary, non-rhythmic flowing movements.

Cognition: progressive executive dysfunction followed by dementia.

Psychiatric features: depression, irritability, apathy, behavioural disturbance and sometimes psychosis.

Family history: usually positive because of autosomal dominant inheritance.

Pathology: degeneration of the caudate and putamen.

Imaging: caudate atrophy may lead to enlargement of the frontal horns of the lateral ventricles.

Diagnosis: genetic demonstration of expanded CAG repeats in HTT.

Treatment of chorea: VMAT2 inhibitors such as tetrabenazine or deutetrabenazine are important modern options.

Antipsychotics: may reduce chorea and are particularly useful when psychiatric or behavioural symptoms coexist.

Chlorpromazine: can suppress chorea but is an older treatment and is not usually the main modern first-choice drug specifically for chorea.

Key Clinical Pattern

Remember Huntington disease as:

Autosomal dominant + adult onset + chorea + psychiatric disturbance + progressive dementia.

The genetic mechanism is:

Chromosome 4 HTT gene → CAG repeat expansion → abnormal huntingtin protein → striatal neurodegeneration.

The classic pathological structure is:

Caudate nucleus atrophy.

And the major treatment update is:

Troublesome chorea → think VMAT2 inhibition, especially tetrabenazine or deutetrabenazine, rather than chlorpromazine alone.