Q fever outbreak in a slaughterhouse in Brazil: description and decade-later investigation.

PURPOSE: To describe the first Q fever outbreak in Brazil and the long-term clinical and serological outcomes of affected individuals ten years after the outbreak. METHODS: A follow-up investigation was conducted among patients involved in a Q fever outbreak that occurred in 2015 in a slaughterhouse in Barbosa, São Paulo State, Brazil. Clinical records from the acute phase were reviewed, and patients were reevaluated ten years later through clinical assessment, review of medical history, serological testing, and molecular analysis. RESULTS: The outbreak affected 17 of 40 slaughterhouse workers (attack rate = 42.5%) and was likely associated with the inhalation of Coxiella burnetii during the slaughter of pregnant cows. Patients presented with prolonged fever, headache, myalgia, pneumonia, hepatitis, and hematuria; six required hospitalization. Ten years later, 14 patients were reevaluated. Of these, 10 developed complications compatible with chronic Q fever, including cardiac and respiratory disorders, as well as persistent fatigue. One woman experienced a premature birth after becoming pregnant following the outbreak. In 2025, one patient presented a phase I antibody endpoint titer of 1:1024 and a history of endocarditis, suggesting persistent infection. CONCLUSION: This study provides a unique description of the long-term clinical and serological outcomes of workers involved in the first documented Q fever outbreak in Brazil and emphasizes the importance of post-outbreak surveillance and prolonged clinical follow-up.