Smear-negative pulmonary tuberculosis (PTB) in Malawi: Are we over-treating?

The fourfold increase in tuberculosis registrations in Malawi over the last decade includes a disproportionate rise in sputum smear-negative PTB cases. Smear-negative PTB in Malawi is diagnosed using clinical guidelines: cough for more than three weeks; three negative AAFB sputum smears; weight loss; no response to an appropriate antibiotic and chest x-ray consistent with PTB. Mycobacterial cultures are not routinely available in Malawi so it has been difficult to establish whether these patients receive TB treatment appropriately. This study used detailed clinical assessment with bronchoscopy and broncho-alveolar lavage (BAL) to investigate the aetiology of respiratory symptoms in patients who would otherwise be commenced on smear-negative PTB treatment. Pre-and post-bronchoscopy sputums and BAL were cultured for mycobacteria. BAL was also cultured on fungal media and examined for Pneumocystis carinii by indirect immunofluorescence. Blood was cultured for bacteria, fungi and mycobacteria and consent sought ror HIV testing. Of 251 smear-negative PTB suspects assessed (November 1997 - March 1998) 220 remained PTB suspects on clinical grounds. Repeat sputum smear was AAFB-positive in 54 patients (22%) and lymph node aspirate AAFB-poative in 4 patients (1.6%). Of the remaining 'true' smear-negatives, 40 patients (16%) had TB microbiologically confirmed by either BAL/sputum AAFB smear and/or culture, and a further 6 (2%) patients had lymphocytic exudative pleural effusions consistent with TB and are improving on TB treatment. Pneumocystis carinii was present in 8 of 120 patients undergoing BAL, endobronchial Kaposis sarcoma in 7 and Cryptococcus neoformans in 3 patients. 183 of 207 patients (88%) were HIV positive.Less than half of those patients to be registered with smear-negative PTB have TB confirmed microbiologically.