Lack of correlation of Brucella antibody titers with clinical outcomes and culture positivity of brucellosis

BACKGROUND: Brucellosis is a zoonotic disease caused by Brucella spp., namely B. melitensis and B. abortus in humans. Culturing is the gold standard method for diagnosis; however, because Brucella is a slow-growing bacterium, which may delay diagnosis, other faster methods, such as serology, are used. Studies on the correlation between Brucella antibody titers and clinical outcomes are limited. Therefore, this study assessed such correlation and evaluated the correlation between baseline serological results with culture positivity and clinical picture. METHODS: Patients tested positive for Brucella antibodies at baseline and diagnosed with brucellosis between January 2008 and December 2018 were included. Collected data included clinical outcomes, baseline culture positivity (growth in culture), arthralgia, baseline and end of therapy (EOT) temperature, white blood cell count, C-reactive protein level, and erythrocyte sedimentation rate. RESULTS: Of 695 patients tested for Brucella antibodies, only 94 had positive baseline serology and diagnosed with acute brucellosis, among whom 63 had EOT serology. No significant correlations were found between EOT antibody titers of both Brucella spp. and clinical cure, mortality, length of stay, and duration of therapy. Additionally, no correlations were found between baseline serology and culture positivity, arthralgia, temperature, and other lab values. CONCLUSION: Brucella serology does not correlate with clinical outcomes at EOT nor with culture positivity at baseline. Therefore, healthcare providers are advised to consider the whole clinical picture of a brucellosis patient without relying solely on serological results during follow up and not replace culturing with serology testing alone at the time of diagnosis.