Annual risk of tuberculous infection measured using serial skin testing, Orel Oblast, Russia, 1991-2005

To compare trends in direct annual risk of tuberculous infection (ARTI) during 1991-2005 in relation to tuberculosis (TB) incidence and to indirect estimates of ARTI derived from the prevalence of tuberculin skin test (TST) positivity in schoolchildren in Orel Oblast, Russia.

In 2005, we abstracted annual TST results and vaccination histories from a representative sample of schoolchildren in Orel Oblast, Russia, where bacille Calmette-Guerin (BCG) vaccination and annual TST of children are nearly universal. We calculated direct ARTI based on the percentage of children tested with TST conversions each year, excluding conversions following BCG vaccination.

We analysed records from 13 206 children, with a median of 10 recorded TST results per child. The ARTI increased from 0.2% in 1991 to 1.6% in 2000, paralleling trends in TB incidence. Similar results were observed when the ARTI was estimated based on prevalence of infection among children aged 3-5 years using a 12 mm cut-off to define TST positivity. Results differed substantially when 10 or 15 mm cut-offs were used or when prevalence was determined among children aged 6-8 years.

ARTI measured through TST conversion increased as TB incidence increased in Orel Oblast. ARTI measured through serial TSTs can thus provide an indicator of changing trends in TB incidence.