Sputum smear-positive tuberculosis: empiric evidence challenges the need for confirmatory smears

To determine the frequency of single scanty or positive sputum smear results and its impact on the surveillance definition of sputum smear-positive tuberculosis (TB).

Moldova, Mongolia, Uganda and Zimbabwe.

A representative sample of laboratories was selected in each country. Data were double-entered and discordances resolved by rechecking the register.

The dataset comprised 128808 examinees with valid information from 23 laboratories in Moldova, all 31 in Mongolia, 30 in Uganda and 23 in Zimbabwe, each covering at least one calendar year. The reason for the examination was diagnostic for 89362, of which 15.2% (n = 13577) were defined as laboratory cases with at least one bacillus on at least one examination. Cases were confirmed by another examination in 72.6% (n = 9861). Of the 9014 cases who had a full set of three examinations, confirmation was obtained in 92.4% (n = 8325).

One quarter of laboratory cases had no confirmatory result, almost entirely attributable to not examining another specimen. The current definition of sputum smear-positive TB requires two positive smears or one positive smear result plus more complex confirmatory evidence. Accepting a single positive examination as sufficient for the definition would greatly increase the sensitivity of the surveillance definition without sacrificing its specificity.