Factors associated with sputum culture conversion in patients with pulmonary tuberculosis

Abstract

Objective: The aim of this study was to determine what factors are associated with sputum culture conversion after 1 month of tuberculosis (TB) treatment.

Materials and methods: A total of 52 patients with new drug susceptible pulmonary TB were included in the study. Patients completed St. George respiratory questionnaire (SGRQ), they were asked about smoking, alcohol use, living conditions and education. Body mass index (BMI) measurements, laboratory tests (C reactive protein [CRP], vitamin D, albumin) were performed, and chest X-ray was done. After 1 month of treatment sputum culture was repeated.

Results: Culture conversion after 1 month of treatment was found in 38.5% cases. None of investigated social factors appeared to have an effect on conversion, but worse overall health status (as reported in SGRQ) and longer duration of tobacco smoking were detected in the "no conversion" group. Concentrations of albumin, CRP, X-ray score and the time it took Mycobacterium tuberculosis culture to grow also differed. Patients who scored 30 or more on SGRQ were more than 7 times as likely to have no conversion. However, the most important factor predicting sputum culture conversion was sputum smear grade at the beginning of treatment: patients with grade of 2+ or more had more than 20-fold higher relative risk for no conversion. Using receiver operating characteristic curve analysis, we also developed a risk score for no conversion.

Conclusions: The most important factors in predicting sputum culture conversion after 1 month of treatment were grades of acid-fast bacilli in sputum smears at time of diagnosis and scores of SGRQ.

Keywords: Culture conversion; Smear grade; Smoking; St. George respiratory questionnaire; Tuberculosis.