Haemophilus ducreyi is the causative agent of which sexually transmitted infection?

• A. Chancroid
• B. Lymphogranuloma venereum
• C. Trachoma
• D. Whooping cough

Answer: (A)

Haemophilus ducreyi causes chancroid, an STI that presents with painful genital ulcers and tender, often suppurative, inguinal lymphadenopathy. This organism is a small, fastidious Gram-negative coccobacillus that grows best on enriched media (such as chocolate agar) in an environment with CO2, which is why culture can be challenging and diagnosis is often supported by molecular tests or clinical presentation. The other conditions listed are caused by different pathogens and have distinct clinical pictures: lymphogranuloma venereum is due to Chlamydia trachomatis L1–L3; trachoma is also caused by Chlamydia trachomatis but affects the eyes; whooping cough is caused by Bordetella pertussis.