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Supervised and induced sputum among patients with smear-negative pulmonary tuberculosis

¹ Tuberculosis and Chest Service, Centre for Health Protection, Departrment of Health, and ² Tuberculosis and Chest Unit, Grantham Hospital, Hong Kong, China.

CORRESPONDENCE: K. C. Chang, Wanchai Chest Clinic, 1st Floor, Wanchai Polyclinic, 99, Kennedy Road, Wanchai, Hong Kong, China. Fax: 852 28346627. E-mail: kc_chang{at}dh.gov.hk

Keywords: Culture, diagnosis, induced sputum, supervised sputum, tuberculosis

Received: September 17, 2007
Accepted December 25, 2007

Sputum culture is essential for monitoring drug resistance. Although sputum induction may optimise culture yield, better selection criteria and simpler algorithms are needed for countries with intermediate tuberculosis burdens.

From a cohort of 660 patients who registered for antituberculosis treatment in a government chest clinic from May 21, 2005 to February 28, 2007, 187 patients with pulmonary disease and a negative smear in two unsupervised sputum specimens were enrolled prospectively for collection of one specimen each of supervised and induced sputum in succession.

Among enrolled patients, induced sputum significantly improved ease of expectoration on a subjective five-point scale. Among 78 patients with culture-proven pulmonary tuberculosis, analysis of matched sputum culture results showed that: 1) induced sputum outperformed supervised sputum; 2) the second unsupervised sputum was significantly inferior to the first and redundant in the presence of the others; 3) adding one specimen each of supervised and induced sputum to two unsupervised specimens increased culture yield significantly; and 4) patients with either extent of disease less than right upper lobe or no respiratory symptoms were more likely to benefit.

In summary, it may be practical to collect a sample of unsupervised, supervised and induced sputum for smear-negative patients with extent of disease less than the right upper lobe, especially when respiratory symptoms are absent.