Smear-negative, culture-positive pulmonary tuberculosis among patients with chronic cough in Cotonou, Benin.

Setting: The main tuberculosis (TB) centre in Benin, West Africa, where only 2% of adult pulmonary TB cases are sputum smear-negative, all other pulmonary cases being smear-positive.

Objectives: To assess the burden of smear-negative, culture-positive pulmonary TB among TB suspects in Cotonou, and to estimate the total number of non-smear-positive TB cases at country level.

Design: For 1 year, one morning sputum culture was performed for every TB suspect (cough lasting >3 weeks, as defined in Benin's national guidelines) with three negative sputum smears (fluorescence technique).

Results: Of 214 TB suspects for whom culture was performed, only 22 smear-negative, culture-positive cases were identified. During the same period, 831 sputum smear-positive cases were diagnosed. Culture therefore contributed only 2.6% of the total number of bacteriologically proven cases.

Conclusion: These results show the relatively low input of culture in TB diagnosis among chronic coughers in Cotonou, Benin, and demonstrates that the expected number of non-smear-positive TB cases in Benin is probably much lower than the World Health Organization's current annual estimates.