Prolonged positivity of sputum smears with negative cultures during treatment for pulmonary tuberculosis

Acid-fast bacilli (AFB) microscopy of sputum smears is the most widely used tool for both diagnosing pulmonary tuberculosis (PTB) and monitoring treatment response. It is not uncommon for patients who show clinical improvement to have prolonged positivity of sputum smears (i.e., ≥60 days after initiation of treatment) with corresponding negative cultures.

To assess treatment outcomes and characteristics associated with prolonged smear-positive, culture-negative status.

A retrospective review was performed of all patients seen by the Cuyahoga County TB Program in Cleveland from 2000 to 2009. There were 159 consecutive smear-positive, drug-susceptible PTB cases with sufficient analyzable bacteriologic, clinical and radiographic data for study.

A smear-positive, culture-negative pattern was seen in 51 patients (32.1%) ≥2 months after initiation of treatment. Age ≥46 years and extent of baseline chest X-ray abnormality were both significantly associated with a prolonged smear-positive, culture-negative pattern. No patients were culture-positive for Mycobacterium tuberculosis after ≥2 months. There was no increased risk of death in the prolonged smear-positive, culture-negative group, and no confirmed relapses.

In our population of patients, in the absence of clinical or radiographic evidence of deterioration, late smear positivity usually has no clinical significance and requires no specific action.