Frequency of isolated positive sputum cultures among pulmonary tuberculosis patients.

Objective: The occurrence of isolated positive sputum cultures among pulmonary tuberculosis (PTB) patients during treatment is not widely reported. This study describes the frequency of isolated positive sputum cultures among PTB patients after initiation of chemotherapy.

Methods: Fifty sputum culture positive PTB patients, consisting of 38 (76%) males and 12 (24%) females with a mean age of 34.31 +/- 19.54 (13-75) years, were studied prospectively over a period of 10 months (September 1999 to June 2000) at Sahary Chest Hospital, Riyadh, Kingdom of Saudi Arabia. The majority of patients received standard 4-drug short-course antimicrobial chemotherapy. Weekly sputum smears and cultures were carried out for each patient during the treatment.

Results: Isolated positive sputum cultures were encountered in 4 (8%) of the studied patients. Two of them had 2 consecutive positive smears and cultures in their third and fourth week during treatment and were attributed to poor compliance to the treatment. Of the remaining 2 patients, one had single isolated culture in his fourth week, while the fourth patient showed a slight growth in the fifth week of the treatment. Due to the undetermined status of the smear and very few colonies in the culture, these 2 isolated cultures were attributed to the carry-over contamination during the laboratory procedures. The same treatment was continued with strict monitoring of compliance to the treatment and laboratory protocols. All of the 4 patients converted to negative before leaving the hospital.

Conclusion: Isolated positive sputum cultures might appear (infrequently) during treatment either due to the treatment noncompliance or carry over contamination. However, under either circumstance, the same treatment should be continued along with strict monitoring of treatment compliance and specimen decontamination and related laboratory protocols.