Non-conversion of sputum culture among patients with smear positive pulmonary tuberculosis in Cameroon: a prospective cohort study

BACKGROUND We investigated the determinants of sputum culture non-conversion following intensive phase of treatment, and assessed the effects on the outcome among patients treated for a first episode of smear positive tuberculosis (TB). METHODS This was a prospective cohort study spanning October 2009 to May 2012, among patients treated for a first episode of smear positive pulmonary tuberculosis in the Chest service of the Yaounde Jamot Hospital, Cameroon. Logistic regressions models were used to relate baseline characteristics with non-conversion of sputum cultures after the intensive phase of treatment. RESULTS A total of 953 patients were admitted to the service during the study period, including 97 (10.2%) who had a positive sputum smear at the end of the intensive phase of anti-tuberculosis treatment. Eighty-six patients with persistent of smear positive sputa at the end of intensive phase of TB treatment were included, among whom 46 (53%) had positive sputum culture for Mycobacterium tuberculosis (C+). The absence of haemoptysis [adjusted odd ratio 4.65 (95% confidence intervals: 1.14-18.95)] and current smoking [7.26 (1.59-33.23)] were the main determinants of sputum culture non-conversion. Of the 46C + patients, 7 (15%) were resistant to at least one anti-tuberculosis drug. Treatment failure rate was 28% among C + patients and 8% among C- patients (p = 0.023). The sensitivity and specificity were 78.6% and 55.4% for culture non-conversion after intensive treatment, in predicting anti-TB treatment failure. CONCLUSIONS Failure rate is high among patients with positive sputum culture after intensive treatment, even in the absence of multi-drug resistant bacilli. Treatment should be closely monitored in these patients and susceptibility to anti-tuberculosis drugs tested in the presence of persistent positive smears following the intensive phase of treatment.