<i>Brucella melitensis</i> sacroiliitis as an unusual culprit for fever of unknown origin (FUO)

Brucellosis is a zoonotic disease that frequently involves the musculoskeletal, reticuloendothelial and neurological systems. We present the case of a male in his early 20s from central India who presented to our outpatient department with a 3-month history of fever, right-sided lower backache and weight loss. A preliminary panel of investigations was unremarkable. However, imaging revealed lymphadenopathy with right-sided sacroiliitis. Despite negative baseline serology (standard agglutination test) and culture, a strong index of suspicion for brucellosis was maintained due to retrospectively elicited history of cattle exposure. This led us to consider an immunocapture agglutination test, which was strongly positive. Subsequently, baseline blood culture was retained for prolonged incubation, yielding <i>Brucella melitensis</i> This case underscores the importance of considering brucellosis as a differential for fever of unknown origin when preliminary diagnostics fail to yield a result.