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

Sputum microscopy for acid-fast bacilli (AFB), although relatively insensitive, is still the cornerstone of tuberculosis (TB) diagnosis in the developing world. Its diagnostic value has been eroded owing to the increasing number of HIV-related smear-negative pulmonary TB cases. Concentration of sputum by centrifugation after liquefaction with sodium hypochlorite is a possible means of increasing the sensitivity of direct microscopy. This procedure has been studied recently in developing countries although with conflicting 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 cohort of consecutive patients with suspected pulmonary TB. We show that the overall sensitivity increased from 54.2% using conventional direct microscopy to 63.1% after concentration (P<0.0015). In HIV-positive patients, sensitivity increased from 38.5% before to 50.0% after concentration (P<0.0034). The significant increase in yield of AFB in HIV-positive patients suggests that this method has a place in routine diagnosis of pulmonary TB in countries with a high prevalence of HIV.