Rationale: Treatment with substantial doses of oral corticosteroids (OCS) for prolonged periods increases the risk of tuberculosis (TB). However, little is known about the effect of inhaled corticosteroids (ICS) in this respect.
Objectives: We quantified the independent contribution of ICS to the risk of TB in a population of patients with airway diseases.
Methods: A population-based cohort design with a nested case-control analysis was used. A cohort of patients with airways disease was formed using the Quebec databases. TB cases were identified and age-matched control subjects were selected from all subjects who entered the cohort in the same month as the cases. TB incidence among the cohort was compared with the general population of Quebec using the standardized incidence ratio.
Measurements and main results: The cohort consisted of 427,648 subjects. There were 564 cases of TB identified between 1990 and 2005. The standardized incidence ratio was 3.9 (95% confidence interval [CI], 2.6-5.4). Any and current users of ICS are at an increased risk of TB (rate ratio [RR], 1.27; 95% CI, 1.05-1.53; and RR, 1.33; 95% CI, 1.04-1.71, respectively). Among users of OCS, no significant relationship could be demonstrated. Among subjects without OCS exposure, adjusted RRs were significant for any ICS use (RR, 1.26; 95% CI, 1.02-1.56) and current use (RR, 1.48; 95% CI, 1.11-1.97) and at the current high dose exposure level (RR, 1.97; 95% CI, 1.18-3.3).
Conclusions: Exposure to ICS is not associated with risk of TB in the presence of OCS but is associated with increased TB risk in nonusers of OCS.