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Infectious Diseases and Microbiology: Rash and Fever
Basics
Description
Rash refers to temporary skin eruptions that accompany localized or generalized infectious diseases. This topic emphasizes the differential diagnosis and early recognition of potentially life-threatening generalized eruptions.
Approach to the Patient
A detailed history should assess immune status, full medication list, travel history, immunization record, exposure to pets or animals, arthropod bites, cardiac abnormalities, prosthetic material, recent contact with ill persons, and possible sexually transmitted infections. Clarify the initial site of rash, pruritus or pain, and speed and direction of spread. Document associated symptoms including prodrome, fever, and itching. Physical examination should define lesion morphology (macules, papules, vesicles, plaques, nodules), configuration (annular, target), arrangement, and distribution (central versus peripheral).
Epidemiology
Infectious mononucleosis may present with generalized maculopapular, petechial, or urticarial rash, often after antibiotic exposure. Approximately one-fifth of erythema infectiosum cases occur in adults, though rash may resemble rubella. Up to half of patients with primary HIV infection develop a maculopapular rash within days of fever onset, typically involving the upper trunk and face. Rubella has been declared eliminated in the United States. Cutaneous leishmaniasis affects up to 1.5 million individuals annually worldwide. Rash occurs in about half of dengue cases. In early Lyme disease, erythema migrans develops at the tick bite site in most patients.
General Prevention
Women of reproductive age should be immunized against rubella. Pregnant women diagnosed with early rubella infection should receive counseling regarding fetal risks and management options.
Etiology
Common adult rash patterns include centrally distributed maculopapular eruptions (such as dengue, infectious mononucleosis, leptospirosis, Lyme disease, primary HIV infection, rubella, measles, typhoid fever, systemic lupus erythematosus, and various rickettsial infections), peripheral eruptions (including bacterial endocarditis, chronic meningococcemia, disseminated gonococcal infection, erythema multiforme, Rocky Mountain spotted fever, and secondary syphilis), confluent desquamative erythemas (graft-versus-host disease, Kawasaki disease, scarlet fever, staphylococcal and streptococcal toxic shock syndromes), vesiculobullous eruptions (disseminated Vibrio vulnificus infection, ecthyma gangrenosum, rickettsialpox), nodular eruptions (disseminated fungal or mycobacterial infections, erythema nodosum, Sweet syndrome), and purpuric eruptions (acute or chronic meningococcemia, disseminated gonococcal infection, enteroviral petechiae, Rocky Mountain spotted fever, thrombotic thrombocytopenic purpura).
Diagnosis
Rocky Mountain spotted fever (RMSF) typically presents with rash around day four of illness, beginning as blanching macules that may progress to purpura and necrosis; genital involvement may be suggestive. Rash may be absent in some cases and is associated with worse prognosis. Meningococcal disease often produces petechiae that evolve into palpable purpura, though other lesion types can occur. Fulminant meningococcemia with disseminated intravascular coagulation constitutes Waterhouse–Friderichsen syndrome. Cutaneous findings in infective endocarditis include vascular phenomena such as petechiae, splinter hemorrhages, and Janeway lesions, and immunologic signs such as Osler nodes and Roth spots. Lyme disease progresses from erythema migrans to neurologic or cardiac involvement and later arthritis or chronic skin changes. Ehrlichiosis often features headache and high fever, with variable rash. Staphylococcal toxic shock syndrome presents with diffuse erythematous rash resembling sunburn, followed by desquamation within two weeks, along with conjunctival injection, mucosal hyperemia, and strawberry tongue. Streptococcal toxic shock syndrome often arises from invasive soft-tissue infection. Dengue rash is typically maculopapular and appears within several days of illness onset.
Diagnostic Tests and Interpretation
Laboratory Studies
Gram stain and culture of pustular or bullous lesions should be performed when infection is suspected. Antibodies to Rickettsia rickettsii become detectable after the first week of RMSF. Meningococcal disease is confirmed by Gram stain and culture of blood or cerebrospinal fluid; skin biopsy may assist. Streptococcal toxic shock syndrome more commonly involves bacteremia than staphylococcal toxic shock syndrome.
Diagnostic Procedures/Other
Skin biopsy with culture and histopathologic examination may establish diagnosis in unclear cases.
Differential Diagnosis
Desquamating erythroderma is more common in staphylococcal than streptococcal toxic shock syndrome. Gonococcemia frequently causes a pustular hemorrhagic rash but may present with diverse lesion types.
Treatment
Management depends on the underlying etiology and may require urgent antimicrobial or supportive therapy.
Ongoing Care and Follow-Up
Serial documentation of rash progression with photography or ink demarcation can assist monitoring.
Complications
Untreated Rocky Mountain spotted fever carries high mortality, underscoring the importance of early recognition and treatment.
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Basics
Description
Rash refers to temporary skin eruptions that accompany localized or generalized infectious diseases. This topic emphasizes the differential diagnosis and early recognition of potentially life-threatening generalized eruptions.
Approach to the Patient
A detailed history should assess immune status, full medication list, travel history, immunization record, exposure to pets or animals, arthropod bites, cardiac abnormalities, prosthetic material, recent contact with ill persons, and possible sexually transmitted infections. Clarify the initial site of rash, pruritus or pain, and speed and direction of spread. Document associated symptoms including prodrome, fever, and itching. Physical examination should define lesion morphology (macules, papules, vesicles, plaques, nodules), configuration (annular, target), arrangement, and distribution (central versus peripheral).
Epidemiology
Infectious mononucleosis may present with generalized maculopapular, petechial, or urticarial rash, often after antibiotic exposure. Approximately one-fifth of erythema infectiosum cases occur in adults, though rash may resemble rubella. Up to half of patients with primary HIV infection develop a maculopapular rash within days of fever onset, typically involving the upper trunk and face. Rubella has been declared eliminated in the United States. Cutaneous leishmaniasis affects up to 1.5 million individuals annually worldwide. Rash occurs in about half of dengue cases. In early Lyme disease, erythema migrans develops at the tick bite site in most patients.
General Prevention
Women of reproductive age should be immunized against rubella. Pregnant women diagnosed with early rubella infection should receive counseling regarding fetal risks and management options.
Etiology
Common adult rash patterns include centrally distributed maculopapular eruptions (such as dengue, infectious mononucleosis, leptospirosis, Lyme disease, primary HIV infection, rubella, measles, typhoid fever, systemic lupus erythematosus, and various rickettsial infections), peripheral eruptions (including bacterial endocarditis, chronic meningococcemia, disseminated gonococcal infection, erythema multiforme, Rocky Mountain spotted fever, and secondary syphilis), confluent desquamative erythemas (graft-versus-host disease, Kawasaki disease, scarlet fever, staphylococcal and streptococcal toxic shock syndromes), vesiculobullous eruptions (disseminated Vibrio vulnificus infection, ecthyma gangrenosum, rickettsialpox), nodular eruptions (disseminated fungal or mycobacterial infections, erythema nodosum, Sweet syndrome), and purpuric eruptions (acute or chronic meningococcemia, disseminated gonococcal infection, enteroviral petechiae, Rocky Mountain spotted fever, thrombotic thrombocytopenic purpura).
Diagnosis
Rocky Mountain spotted fever (RMSF) typically presents with rash around day four of illness, beginning as blanching macules that may progress to purpura and necrosis; genital involvement may be suggestive. Rash may be absent in some cases and is associated with worse prognosis. Meningococcal disease often produces petechiae that evolve into palpable purpura, though other lesion types can occur. Fulminant meningococcemia with disseminated intravascular coagulation constitutes Waterhouse–Friderichsen syndrome. Cutaneous findings in infective endocarditis include vascular phenomena such as petechiae, splinter hemorrhages, and Janeway lesions, and immunologic signs such as Osler nodes and Roth spots. Lyme disease progresses from erythema migrans to neurologic or cardiac involvement and later arthritis or chronic skin changes. Ehrlichiosis often features headache and high fever, with variable rash. Staphylococcal toxic shock syndrome presents with diffuse erythematous rash resembling sunburn, followed by desquamation within two weeks, along with conjunctival injection, mucosal hyperemia, and strawberry tongue. Streptococcal toxic shock syndrome often arises from invasive soft-tissue infection. Dengue rash is typically maculopapular and appears within several days of illness onset.
Diagnostic Tests and Interpretation
Laboratory Studies
Gram stain and culture of pustular or bullous lesions should be performed when infection is suspected. Antibodies to Rickettsia rickettsii become detectable after the first week of RMSF. Meningococcal disease is confirmed by Gram stain and culture of blood or cerebrospinal fluid; skin biopsy may assist. Streptococcal toxic shock syndrome more commonly involves bacteremia than staphylococcal toxic shock syndrome.
Diagnostic Procedures/Other
Skin biopsy with culture and histopathologic examination may establish diagnosis in unclear cases.
Differential Diagnosis
Desquamating erythroderma is more common in staphylococcal than streptococcal toxic shock syndrome. Gonococcemia frequently causes a pustular hemorrhagic rash but may present with diverse lesion types.
Treatment
Management depends on the underlying etiology and may require urgent antimicrobial or supportive therapy.
Ongoing Care and Follow-Up
Serial documentation of rash progression with photography or ink demarcation can assist monitoring.
Complications
Untreated Rocky Mountain spotted fever carries high mortality, underscoring the importance of early recognition and treatment.
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