Sputum Conversion among Patients with Pulmonary Tuberculosis: Are Two Weeks Enough for Respiratory Isolation?

Background : Surgical mask should be used to reduce aerosols generated from known infectious pulmonary tuberculosis patient. WHO and the United States CDC recommend that the patient should have received standard multi-drug anti-tuberculosis therapy for at least 2 weeks and had 3 consecutive AFB-negative smear of sputum specimens before stopping respiratory isolation. Such sputum smear was routinely performed at 2 months. Objective : To explore the sputum conversion rate at 2 weeks in the patients with smear positive pulmonary tuberculosis and risk factors for persistent positive sputum results. Material and method : A prospective cohort study in 76 recent diagnosed pulmonary tuberculosis patients with positive smear was conducted in Lampang Hospital between October 2010 and May 2011. Sputum was collected for AFB smear and culture at 2 weeks after starting treatment. The sputum conversion rate was calculated. Risk factors for persistent positive sputum results were analyzed by Fisher’s exact test and logistic regression. Results : 77.6% of the patients were male. The mean age was 52.7 ± 17.8 years (range, 18 - 91). At 2 weeks of initial therapy, 55.3 % and 39.5 % of the patients had persistent positive sputum smear and culture respectively. On stepwise multiple regression analysis, presence of lung cavitation (OR = 5.07, 95%CI 1.40 - 18.39, p = 0.014) and +3 AFB smear grade at the initial treatment (OR = 20.27, 95%CI 1.59 - 258.76, p = 0.021) were the factors independently associated with persistent positive sputum culture results. Conclusion : Respiratory isolation period of two weeks is not enough for pulmonary tuberculosis patient with positive smear sputum, especially in which lung cavitation or highly smear grade on the initial treatment was found. Keywords : Pulmonary tuberculosis, Sputum conversion, Surgical mask, Respiratory isolation