Melioidosis — DTM&H MCQ

Correct answer: D — Melioidosis

The correct answer is D, melioidosis. Melioidosis is caused by Burkholderia pseudomallei, a soil dwelling Gram-negative bacillus classically described with bipolar (safety pin) staining, and diabetes is the single strongest risk factor for severe or disseminated disease. Northern Thailand during the rainy season is a highly endemic setting where inoculation occurs through skin contact with contaminated soil or water, or by inhalation, leading to pneumonia with haematogenous seeding of multiple visceral abscesses, especially in the spleen and liver. This combination of geography, diabetes, pneumonia and multiple splenic abscesses with a bipolar staining Gram-negative bacillus on blood culture is the classic exam vignette for melioidosis, which UKHSA laboratory guidance identifies by isolation as the diagnostic gold standard. Why the other options are wrong: E. Pneumonic plague: Yersinia pestis also shows bipolar staining but causes an acute, rapidly fatal illness typically linked to flea bite or rodent exposure, not chronic splenic abscess formation, and is not endemic to rainy season Thailand. A. Scrub typhus: caused by Orientia tsutsugamushi, an obligate intracellular organism that does not grow on standard blood culture and produces fever with eschar and lymphadenopathy, not a culturable Gram-negative bacillus with abscesses. C. Brucellosis: causes fever and occasionally splenic abscesses but the organism is a small Gram-negative coccobacillus without bipolar staining, and it is linked to unpasteurised dairy or animal contact rather than Thai soil exposure. B. Disseminated histoplasmosis: is a dimorphic fungus, not a Gram-negative bacillus, and would not grow as a bacterium on blood culture. Key point: In a diabetic returning from South East Asia with pneumonia, splenic abscesses and a bipolar staining Gram-negative bacillus on culture, think melioidosis (Burkholderia pseudomallei) until proven otherwise.

Reference: UK Health Security Agency, Laboratory diagnosis of melioidosis, UKHSA Research Portal, https://researchportal.ukhsa.gov.uk/en/publications/laboratory-diagnosis-of-melioidosis