Katayama fever — DTM&H MCQ

Correct answer: C — Schistosoma serology

Explanation lettering: D = shown as B · E = shown as C · C = shown as D · B = shown as E

Schistosoma serology (E) is the most appropriate next investigation. This traveller has classic Katayama syndrome: fever, urticaria, cough and eosinophilia several weeks after freshwater exposure in sub-Saharan Africa, occurring before egg-laying begins. Current UK guidance notes that seroconversion in acute schistosomiasis usually occurs between 4 and 8 weeks after exposure, whereas stool and urine microscopy for ova are frequently negative at this stage because adult worms have not yet matured and started oviposition. Serology therefore has far greater sensitivity than microscopy in the acute (pre-patent) phase and is the recommended test to confirm the diagnosis and guide early praziquantel treatment. Why the other options are wrong: A. Widal serology: this test targets typhoid (Salmonella Typhi) agglutinins, is unreliable and non-specific, and has no relevance to a freshwater exposure history with eosinophilia. B. Blood film alone: a blood film is used to detect malaria parasites or microfilariae, but malaria does not cause eosinophilia and this presentation with urticaria and freshwater contact points specifically to schistosomiasis, not a blood-borne parasitaemia. C. Urine culture: this detects bacterial urinary infection, not schistosome ova or antibodies, and would not explain eosinophilia or the systemic allergic features described. D. Dengue IgG alone: dengue is transmitted by mosquitoes, not freshwater contact, does not typically cause marked eosinophilia, and IgG alone cannot reliably time acute infection. Key point: In suspected acute schistosomiasis (Katayama syndrome), serology is more sensitive than stool or urine microscopy because antibody response precedes patent egg excretion by several weeks.

Reference: British Infection Association / Journal of Infection (2024), UK guidelines for the investigation and management of eosinophilia in returning travellers and migrants, section 6.1.1 (Katayama syndrome): seroconversion in acute schistosomiasis occurs between 4 and 8 weeks (up to 22 weeks), with microscopy sensitivity too low to use in isolation. https://www.journalofinfection.com/article/S0163-4453(24)00262-7/fulltext