Quantitative differences in sputum smear microscopy results for acid-fast bacilli by age and sex in four countries.

Objective: To examine the influence of age and sex on the grading of tuberculosis (TB) sputum smear microscopy results.

Setting: Laboratories in Moldova, Mongolia, Uganda and Zimbabwe.

Methods: Data from nationally representative samples of laboratory registers were double-entered and validated, and discordances were resolved by rechecking against the registers.

Results: The dataset comprised 128,808 examinees from 23 laboratories in Moldova, all 31 in Mongolia, 30 in Uganda and 23 in Zimbabwe, each covering at least one calendar year. Among all examinees, 89,362 had a diagnostic examination, 13,577 (15.2%) of whom were cases. A non-quantified positive result was recorded among 1272 (9.4%) of these. Scanty results were most frequent in Zimbabwe (8.5%) and most infrequent in Uganda (1.1%). In contrast, the highest grade, of 3+ positive, was most frequent (43.9%) in Mongolia. The lowest proportion of low-grade positivity was recorded for males aged 15-24 years and the highest among females aged >or=65 years.

Conclusion: Differences in the frequency of low-grade positivity between the four countries were striking. Females tended to have lower bacillary counts, and low-grade positivity was more frequent at the extremes of age. These results reinforce the need for appropriate instructions on how to produce high-quality sputum to improve yield.