What a difference a day makes: same-day vs. 2-day sputum smear microscopy for diagnosing tuberculosis

Setting: Nine district-level microscopy centres in Assam and Tripura, India. Objective: Same-day sputum microscopy is now recommended for tuberculosis (TB) diagnosis. We compared this method against the conventional 2-day approach in routine programmatic settings. Methods: During October-December 2012, all adult presumptive TB patients were requested to provide three sputum samples (one at the initial visit, the second 1 h after the first sample, and the third the next morning) for examination by Ziehl-Neelsen smear microscopy. Detection of acid-fast bacilli with any sample was diagnostic. The first and second spot sample comprised the same-day approach, and the first spot sample and next-day sample comprised the 2-day approach. Results: Of 2168 presumptive TB patients, 403 (18.6%) were smear-positive according to the same-day method compared to 427 (19.7%) by the 2-day method (McNemar's test, P < 0.001). Of the total 429 TB patients, 26 (6.1%) were missed by the same-day method and 2 (0.5%) by the 2-day method. Conclusion: Same-day specimen collection for microscopy missed more TB than 2-day collection. In India, missing cases by using same-day microscopy would translate into a considerable absolute number, hindering TB control efforts. We question the indiscriminate switch to same-day diagnosis in settings where patients reliably return for testing the next day.