Tuberculin testing, BCG and tuberculosis today

Tuberculosis is not simply a problem hanging over from the past—it is a growing challenge—but what are the risks of acquiring tuberculosis infection in childhood, and how should those risks be assessed?

In this issue of Thorax Leung and colleagues¹ analyse the results of tuberculin skin testing in over 21 000 children in Hong Kong aged 6–9 years between October 1999 and February 2000. 99% of the children had received BCG vaccination in the neonatal period. The authors used three different approaches to the data to estimate the subsequent annual risk of tuberculous infection. In broad terms, one approach used the size of the tuberculin response to assess whether infection had occurred, using a cut off point of ≥10 mm induration after skin testing with one unit of tuberculin. They then used age (which equals the number of years each child had been at risk of infection) to estimate the annual risk. This is the “classic” method. The second approach estimated the annual risk of infection by comparing the rates of tuberculin positivity in the 8–9 year old age group with those in the 6–7 year old group. The third estimated the prevalence of infection by locating a secondary peak in the tuberculin reaction distribution curve and assuming that, among those with tuberculosis infection, there would …