The significance of the persistent presence of acid-fast bacilli in sputumsmears in pulmonary tuberculosis

Study objectives: Identification of acid-fast bacilli (AFB) in the sputum s mear at the completion of tuberculosis therapy is in some settings consider ed evidence of treatment failure. However, some patients with pulmonary tub erculosis (TB) will have positive smear results with negative sputum cultur e results at the end of therapy. The objective es of this study were to est imate the prevalence of persisting positive sputum smear I results in patie nts with TB and to identify characteristics that distinguish patients with persistently positive sputum smear results Mho also had negative sputum cul ture results from patients identified as treatment failures,. Design: A population-based, historical cohort study with nested case contro l study. Setting: British Columbia Division of Tuberculosis Control central case reg istry. Patients: All 428 patients with culture-proven pulmonary TB in British Colu mbia over 7 pears with sputum that was positive for AFB, Methods: Review of laboratory data of all 428 patients, as well as clinical data of a subset of 30 patients with persistently positive smear I results beyond 20 weeks. Results: Sputum smears were positive for AFB in 205 patie nts (48%) at 4 weeks, in 30 patients (7%) at 20 weeks, and in 12 patients ( 3%) at 36 weeks. Of the patients with smear results th were persistently po sitive at 20 weeks, 23 (77%) had negative sputum culture results and 7 (23% ) had positive sputum culture results tie, they were treatment failures. Pa tients identified as treatment failures had more localized disease as shown on chest radiographs, had less radiographic improvement at follow-up, had a higher pr prevalence of drug resistance, and were less compliant with med ications than patients a with persistently positive smear I Results and neg ative culture results. No subject with a negative e culture result relapsed over the 6- to 18-month observation period. Conclusion: Sputum that is persistently positive for AFB in patients in dev eloped countries is more likely to be associated with negative culture resu lts than with treatment failure.