Significance of the tuberculin test in Singapore

The standard tuberculin test used by all Singapore government hospitals and institutions is the intradermal Mantoux test using 1 TU of PPD RT23 with Tween 80, and read 72 hours later. There is almost 100% BCG coverage in Singapore children for many years, and therefore the tuberculin skin reaction must be interpreted with special consideration. Taking 8 mm and above as positive, six month old infants vaccinated at birth gave a positive rate of 42% and a mean reaction size of 5.89 mm. The reaction appeared to wane rapidly and among 6 year old school children the positive rate dropped to 12% and the mean size to 2.38 mm. By the age of 11 years, the children showed a positive rate of 36% and a mean size of 6.27 mm. A further increase is observed in 15 year old children, the positive rate being 88% and mean size 13.28 mm. Among tuberculosis contacts, the positive rate and mean size of the tuberculin reaction are generally higher, especially in the younger age groups. Tuberculosis patients above 15 years old were observed to be practically all positive reactors with a mean size of at least 16 mm.