Prevalence of Brucella antibodies on a previously acute brucellosis infected population: sensitivity, specificity and predictive values of Rose Bengal and Wright standard tube agglutination tests.

PURPOSE: Brucellosis is a zoonosis with worldwide distribution. The presence of antibodies after acute infection and the prevalence of positive serology in endemic area are not well documented.
METHODS: Patients hospitalized with acute brucellosis were relocated 3-13 years after the initial infection. Hospital records of the initial infection were retrieved, and examination of Brucella antibodies using Rose Bengal test (RBT) and Wright standard tube agglutination (STA) test was performed.
RESULTS: Eighty-three patients were hospitalized from 2000 to 2010; 50.6 % were farmers and 37.4 % livestock farmers. All had febrile illness and various focal complications. All had positive serology, and 82.2 % had positive blood cultures; 91.5 % were treated with streptomycin plus doxycycline. Seventy-two (86.7 %) were relocated on follow-up. Nine (12.5 %) had positive RBT and STA up to 1/320. Occupational history was associated with positive serology (p = 0.0172), and 8/9 of the positive individuals were livestock farmers (38.0 % of the livestock farmers checked). Residence, years after the infection, clinical presentation of brucellosis and treatment were not associated with serology results. Both tests had excellent sensitivity (nearly 100 %), specificity 87.5 % and excellent negative predictive value (nearly 100 %); however, positive predictive value was only 11.4 %.
CONCLUSIONS: Rapid and low-cost tests as RBT and STA are still very useful in diagnosing acute brucellosis; however, every positive test must be examined together with clinical symptoms and occupational history. The tests can be used as screening tests in endemic populations to rule out acute brucellosis.