Laboratory-Acquired Brucella abortus Infection Mimicking Autoimmune Disease: A Case Report with Genomic Confirmation

Background: Brucellosis is a globally distributed zoonotic disease characterized by highly variable clinical manifestations that may mimic systemic autoimmune and inflammatory disorders. In Europe, where the incidence of brucellosis is relatively low, limited clinical awareness may contribute to delayed diagnosis and inappropriate management. In addition to zoonotic transmission, Brucella species are a well-recognized cause of laboratory-acquired infections (LAIs) among microbiology laboratory personnel. Methods: We report a case of laboratory-acquired Brucella abortus infection in a young woman presenting with undulant fever, arthralgia, systemic inflammation, elevated ferritin levels, and antinuclear antibody (ANA) positivity. Microbiological confirmation was achieved through serological testing (ELISA), repeat blood cultures, species-specific quantitative PCR, and whole-genome sequencing (WGS) followed by core genome multilocus sequence typing (cgMLST). Results: Initial laboratory evaluation revealed elevated C-reactive protein, mildly increased ferritin levels (146 ng/mL), abnormal liver enzyme levels, and rising ANA titers (from 1:160 to 1:320), raising suspicion of a systemic autoimmune disorder and prompting consideration of corticosteroid therapy. Although the initial blood culture was negative, subsequent molecular diagnostics and repeat cultures confirmed B. abortus infection. Epidemiological investigation suggested a possible occupational exposure in a diagnostic microbiology laboratory, consistent with a laboratory-acquired infection. Genomic analysis classified the isolate as sequence type 1 (ST1) and demonstrated zero allelic differences compared with the ST1 reference strain. Targeted antimicrobial therapy resulted in complete clinical recovery, supporting an infection-triggered immune response rather than primary autoimmunity. Conclusions: Acute brucellosis should be considered in the differential diagnosis of febrile syndromes accompanied by autoimmune-like laboratory abnormalities, even in low-incidence regions. This case highlights the diagnostic challenges posed by laboratory-acquired brucellosis and underscores the importance of early microbiological investigation and strict biosafety awareness in laboratory settings.