Misdiagnosis of tuberculosis and the clinical relevance of non-tuberculous mycobacteria in Zambia

Objective: To determine the accuracy of TB diagnosis of TB in Zambia in the era of increasing HIV prevalence. Methods: Sputum of the clinically diagnosed TB cases was additionally subjected to liquid culture and molecular identification. This study distinguished between TB cases confirmed by positive Mycobacterium tuberculosis (M. tuberculosis) cultures and mycobacterial disease caused by non tuberculous mycobacteria (NTM). Results: Only 49% of the 173 presumptively diagnosed TB cases was M. tuberculosis cultured, while in 13% (22) cases, a combination of M. tuberculosis and NTM was found. In 18% of the patients only NTM were cultured. In 28%, no mycobacteria was cultivable. HIV positive status was correlated with the isolation of NTM (P<0.05). Conclusions: The diagnosis of tuberculosis based on symptoms, sputum smear and/or chest X ray leads to significant numbers of false positive TB cases in Zambia, most likely due to the increased prevalence of HIV. The role of NTM in tuberculosis like disease also seems relevant to the false diagnosis of TB in Zambia.