In only half of the tuberculosis cases diagnosed in Zambia, Mycobacterium tuberculosis is the causative agent

Abstract number: O311

Buijtels P.C.A.M., Iseman M.D., Parkinson S., de Graaff C.S., Verbrugh H.A., Petit P.L.C., van Soolingen D.

Diagnosis of tuberculosis (TB) in resource-poor countries is almost exclusively based on microscopy of Ziehl-Neelsen stained (ZN) sputum smears; in some settings supplemented by chest X-ray.

Objectives: The aim of this study was to determine the accuracy of this diagnosis of TB in Zambia in the era of increasing HIV prevalence. By applying MGIT liquid culture technique, this study distinguished between (i) TB cases confirmed by positive Mycobacterium tuberculosis cultures, (ii) mycobacteriosis caused by non-tuberculous mycobacteria (NTM) and, (iii) tuberculosis-like disease caused by organisms other than mycobacteria.

Methods: Adult patients were included who had been diagnosed with TB on basis of respiratory complaints lasting two or more weeks, failure to improve on two courses of empiric antibiotics, a positive ZN sputum smear and/or findings on the chest X-ray consistent with TB. Sputa of the presumptively diagnosed TB cases were subjected to MGIT liquid culture. Mycobacterium isolates were identified using a nucleic acid amplification method and 16S DNA sequencing.

Results: In only 47% of the 187 presumptively diagnosed TB cases was M. tuberculosis cultured. In 19% exclusively NTM were found. In another 12% of the presumptive cases, a combination of M. tuberculosis and NTM was isolated. In the remaining 29% of cases in which TB was diagnosed, no mycobacteria were cultivable. HIV positivity was significantly correlated with the isolation of NTM from sputum and inversely associated with the isolation of exclusively M. tuberculosis (p < 0.05).

Conclusions: Basing the diagnosis of tuberculosis on symptoms, sputum smear and/or chest X-ray may lead to significant numbers of false-positive cases of tuberculosis in Zambia, due to the increased prevalence of HIV.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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