Prevalence of Brucella antibodies after acute brucellosis

Diagnosis of brucellosis is made by a demonstration of high brucella agglutination titer using the Standard Tube Agglutination Test (SAT) in the presence of compatible clinical symptoms. In an endemic area like Saudi Arabia, persistence of brucella antibodies after recovery from acute brucellosis is not uncommon. The aim of this study was to monitor brucella antibody titers after successful treatment and clinical cure, and identify factors influencing their persistence. Patients clinically cured of acute brucellosis, who have at least three serological follow-ups, were reviewed retrospectively. A titer of less than 1:320 was considered a "serological cure". One hundred sixteen (116) patients clinically cured of acute brucellosis were followed up for different lengths of time. All patients had no re-infection or relapse at the end of follow-up. The actuarial life-table analysis showed an increase in proportion of serologically cured from 8.3% in the first three months to 71.4% after two years or more, and the median time for serological cure was 18.5 months (SD = 3 months). In univariate analysis, older age, male gender, and patients treated with less than three antibiotics are more likely to have persistent brucella antibodies of > or = 1:320 (P>0.2). The use of doxycycline in the treatment was associated with serological cure (51.1% vs. 27.5%) (P<0.05). However, with the Cox regression model none of the variables were statistically significant as a prognostic factor for serological cure (P>.05). In conclusion, brucella antibodies of 1:320 or higher can persist for more than 2 years after successful treatment and clinical cure. Re-evaluation of diagnostic titer of brucellosis is required in brucella-endemic countries.