Louse-borne epidemic typhus — DTM&H MCQ

Correct answer: A — Rickettsial PCR or serology with treatment guided by clinical suspicion

The correct answer is A, rickettsial PCR or serology with treatment guided by clinical suspicion. The stem describes classic epidemic typhus (Rickettsia prowazekii): overcrowded cold conditions, heavy body-louse infestation, high fever, severe headache and truncal rash, a pattern specific to louse-borne rickettsial disease rather than the other listed infections. Confirmatory testing in the UK is via the UKHSA Rare and Imported Pathogens Laboratory, which offers acute and convalescent serology and PCR for rickettsial infections. Because serology can be negative early and PCR sensitivity falls once doxycycline is started, empirical doxycycline should be given on clinical and epidemiological grounds without waiting for laboratory confirmation, since delay increases mortality in this louse-borne outbreak setting. Why the other options are wrong: E. Sputum Xpert MTB/RIF: this detects Mycobacterium tuberculosis; it does not explain an acute febrile rash illness clustered with body lice and has no role in an outbreak with this specific vector history. D. Thick blood film for trypanosomes: this diagnoses African trypanosomiasis, which is tsetse-fly transmitted, not louse-borne, and presents with chancre, lymphadenopathy and later neurological features rather than an acute truncal rash outbreak. C. Midday urine microscopy for schistosome ova: this is used for Schistosoma haematobium and requires prior freshwater contact; it is irrelevant to a body-louse associated febrile rash cluster. B. Rapid dengue NS1 testing as the sole test: dengue is mosquito-borne, not consistent with the louse infestation and cold-camp context, and relying on a single rapid antigen test would miss the correct diagnosis and delay life-saving doxycycline. Key point: In a louse-infested, overcrowded, cold-climate outbreak of fever, headache and truncal rash, suspect epidemic typhus and start doxycycline empirically while sending rickettsial serology or PCR for confirmation.

Reference: UKHSA Rare and Imported Pathogens Laboratory (RIPL): provides rickettsial diagnostics including acute and convalescent serology and PCR, with timely doxycycline treatment encouraged in suspected cases (Imported rickettsial infections to the United Kingdom, 2015-2020, Journal of Infection, 2023). https://www.gov.uk/government/collections/rare-and-imported-pathogens-laboratory-ripl