Sputum concentration improves diagnosis of tuberculosis in a setting with a high prevalence of HIV

Sputum microscopy for acid-fast bacilli (AFB), although relatively insensit ive, is still the cornerstone of tuberculosis (TB) diagnosis in the develop ing world. Its diagnostic value has been eroded owing to the increasing num ber of HN-related smear-negative pulmonary TB cases. Concentration of sputu m by centrifugation after liquefaction with sodium hypochlorite is a possib le means of increasing the sensitivity of direct microscopy. This procedure has been studied recently in developing countries although with conflictin g results. The aim of our study, performed in 1996 in Addis Ababa, Ethiopia , was to evaluate the sensitivity of the concentration method in a large co hort of consecutive patients with suspected pulmonary TB. We show that the overall sensitivity increased from 54.2% using conventional direct microsco py to 63.1% after concentration (P < 0.0015). In HIV-positive patients, sen sitivity increased from 38.5% before to 50.0 % after concentration (P < 0.0 034). The significant increase in yield of AFB in HIV-positive patients sug gests that this method has a place in routine diagnosis of pulmonary TB in countries with a high prevalence of HIV.