Background: The incidence of active tuberculosis (TB) among the Cree, an Aboriginal population of Canada, is dropping, but it remains three times that of the general population. We analyzed data from tuberculin skin test (TST) surveys to determine estimates of prevalence of infection and annual risk of infection (ARI) in this population.
Methods: TST surveys targeting 12-year-old students were conducted annually from 1993 to 1998. Students with no record of previous positive TST (> or = 10 mm) were offered TST (5 TU PPD-T). Data collected included result of previous TST reading for all students, readings of TSTs performed (mm induration) and BCG (bacille Calmette-Guérin) vaccination status for those positive on TST.
Results: A total of 1274 children were screened (participation rate 94%). TST reaction size frequency distribution plots a bimodal curve. The prevalence of infection among 12 year olds was 15.3% over this period. ARI estimates range from 0.6 to 2.4% (average ARI 1.4%). A significant downward linear trend in ARI was observed over the period (P < 0.001).
Discussion: Calculated ARI may be over-estimated due to prior BCG vaccination; however, the trend in ARI confirms decreasing transmission of TB infection. Better knowledge of human immunodeficiency virus seroprevalence among pregnant women is needed to complete the evaluation of the BCG program.