Factors Affecting Discordance between Sputum Smear and Culture Conversion Rates In Newly Diagnosed Pulmonary Tuberculosis: A Retrospective Study in Developing Country

Aims: To assess the performance of sputum AFB smear for monitoring treatment response and outcome of anti-tuberculous drugs among newly diagnosed smear positive pulmonary TB patients.
Study Design: This study was conducted prospectively among newly diagnosed smear positive pulmonary TB patients.
Place and Duration of Study: Queen Savang Vadhana Memorial Hospital and Chonburi Regional Hospital, Chonburi province, Thailand during April 2010 and July 2012.
Methodology: Sputum AFB smear, culture and drug susceptibility test were performed at the time of diagnosis, the second and the fifth month of treatment. Baseline characteristic, clinical and laboratory parameters, treatment regimens and adverse events were recorded. Descriptive statistics and multiple logistic regression analysis were applied as appropriate. The performance of sputum AFB smear for monitoring treatment response and outcome of anti-tuberculous drugs was done using culture as the gold standard.
Results: Of 297 eligible pulmonary TB cases, majorities were male (72.4%) with median age of 39 years, illiterate to low educated (52.6%) and earning low income (77.5%). Cough was the most common symptom (91.2%) and cavity was present in 31.1%. At the second month, 17.0% of patients had discordance between sputum AFB smear and culture. High bacilli load (adjusted OR=2.38, CI=1.09-5.18), and hearing alteration (adjusted OR=10.98, CI=1.79-67.28) were significant predictors. Hypoalbuminemia was significantly more severe in patients with false positive AFB smear (P=.04). Sensitivity and specificity for AFB smear were 44.7% and 89.6% at the second month and 57.1% and 97.5% at the fifth month, respectively. MDR-TB was diagnosed in 1.0% and success rate was 77.1%.
Conclusions: Baseline AFB smear ≥ 2+ and hypoalbuminemia as well as adverse events during intensive phase are strongly recommended as the criteria to prioritize culture and DST for new smear positive pulmonary TB patients with positive AFB smear at the second and the third month of treatment in developing countries.