The microbiological diagnosis of tuberculosis in a resource - limited setting: is acid-fast bacilli microscopy alone sufficient?

Abstract

The objective of this study is to audit the processes for the microbiological diagnosis of tuberculosis (TB) in our resource-limited setting. A total of 694 specimens were received from 333 patients. 129 (38.7%) of these patients were positive for TB. 78 (60.5%) were positive on AFB microscopy alone, 13 (10.0%) on culture alone and 38 (29.5%) on both culture and AFB microscopy. Fifty-one (51) cases were positive on culture, 38 of these (74.5%) had growth on Lowensen-Jensen culture medium alone, 11 (19.6%) on Pyruvic Acid Enhanced Medium (PAEM) and 3 (5.9%) on both culture media. AFB microscopy showed a diagnostic specificity of 71.6% and a sensitivity of 74.5%. M. Bovis appears to be prevalent and we suggest the need for speciation. If AFB microscopy is to be routinely used alone, without confirmation by culture, then the overriding need is for quality to be fully assured in its use.

Keywords: Mycobacteria, tuberculosis, accuracy, AFB microscopy, culture