False positive seroreactivity to brucellosis in tuberculosis patients: a prevalence study

Mojtaba Varshochi^1,2, Jafar Majidi², Marjan Amini¹, Kamyar Ghabili³, Mohammadali M Shoja^3
1Department of Infectious Disease, Tabriz University of Medical Sciences, Tabriz, Iran; ²Infectious Disease and Tropical Medicine Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; ³Tuberculosis and Lung Disease Research Center, Tabriz University of Medical Sciences, Tabriz, Iran

Background: The rising worldwide incidence of tuberculosis (TB) increases the demand for knowledge about its potential seroreactivity with other microbial agents. A few reports and the authors’ experiences indicate that tuberculosis may result in a false-positive brucellosis serology. This may cause a diagnostic challenge because of the close clinical resemblance of these two infections.
Objective: The aim of the present prevalence study was to elucidate brucellosis seroreactivity in patients with active TB.
Methods: Ninety-eight patients with newly diagnosed and active TB were studied using an enzyme-linked immunosorbent assay (ELISA) and Wright’s and Coombs–Wright’s tests. Seventy-five healthy individuals were used as controls. The patients showed signs of recovery after starting a standard anti-TB regimen and had no clinical evidence of brucellosis at a subsequent 6-month follow-up. The data were analyzed statistically by Fisher’s exact test using SPSS 11.0.
Results: We found that 9.2% of TB patients versus 1.3% of healthy controls had positive results on the anti-Brucella IgG ELISA (P = 0.04). Five TB patients were found to have agglutination on Wright’s tests, while none of the controls showed agglutination.
Conclusion: Active TB patients may have some seroreactivity with Brucella antigens, and Brucella IgG ELISA may give a false positive in these patients. Clinicians should consider false positive brucellosis seroreactivity in patients with active TB.

Keywords: false positive serology, ELISA, diagnosis