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.