Role of 2-month sputum smears in predicting culture conversion in pulmonary tuberculosis

Abstract

Sputum smears and culture conversion are frequently used to evaluate treatment response in pulmonary tuberculosis patients. Limited data are available on the evaluation of the correlation between under-treatment sputum smear results and culture conversion.This prospective study included sputum culture-proven pulmonary tuberculosis patients at six hospitals in Taiwan. At least two sets of sputum were collected at the completion of 8 weeks of TB treatment. The sensitivities and specificities of 2-month sputum smears were estimated based on culture conversion status.A total of 371 patients were enrolled for analysis. Factors associated with culture conversion included having a smear positive before treatment, presence of a cavity on radiography, rifampicin resistance and usage of the DOTS (directly observed therapy, short course) strategy. The sensitivities of 2-month sputum smears for culture conversion among all patients, initially smear-positive patients and initially smear-negative patients were 64.3, 71.4 and 38%, respectively, and the specificities were 81.6, 69.9 and 92.8%, respectively. In patients who were 2-month sputum smear-positive, the 2-month culture conversion rate was 80% if the patients were under DOTS and without cavitary lesions in radiograms.The predictive value of 2-month sputum smears in culture conversion was limited and highly influenced by clinical factors in pulmonary tuberculosis patients.KEYWORDS: Culture, directly observed therapy short course implementation, Mycobacterium tuberculosis, pulmonary tuberculosis, sputum P ulmonary tuberculosis (PTB) is an airborne infectious disease that requires multiple-drug combination therapy and long treatment duration. Despite great advances in molecular diagnosis, sputum cultures of Mycobacterium tuberculosis (MTB) remain the gold standard for PTB diagnosis. After initiation of anti-tuberculosis (anti-TB) treatment, sputum acidfast bacilli (AFB) smears and cultures of MTB are regularly checked during the treatment period and serve as important indicators of treatment response. Achievement of sputum sterilisation, which is determined by sputum culture conversion, is a cardinal index of treatment success. Previous studies have demonstrated that the time to sputum negativity is an important determinant of relapse [1][2][3]. Failure to achieve sputum culture conversion in ,2 months will lead to a worse treatment outcome [4]. Documentation of sputum culture conversion is also recommended as a necessary criterion before completion of anti-TB treatment in current treatment guidelines [5]. Based on the high predictive value of sputum culture conversion in treatment response [4,6,7], identification of the clinical factors that are associated with a lower sputum culture conversion rate is of crucial importance in PTB management [8][9][10].In spite of the high accuracy of sputum culture conversion in the assessment of treatment response, the long yield time limits its usefulness in clinical practice. As a simple and rapid test, sputum smears are fre...

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