Incidence of pneumocystosis among patients exposed to immunosuppression

Background: The decision to administer prophylaxis to patients receiving immunosuppression against pneumocystosis remains a dilemma. Objective: To determine overall and age-specific 5-year pneumocystosis incidence within a population exposed to immunosuppressants. Methods: Retrospective cohort analysis identifying incident pneumocystosis cases among adults without HIV, AIDS, or cancer exposed to immunosuppressant, corticosteroid therapy, or both. Results: We identified 406 new cases among patients prescribed an immunosuppressant, corticosteroid, or both. Overall incidence of pneumocystosis was 0.012% (406/3,366,086). Incidence was highest in those exposed to immunosuppressant and corticosteroid medications (0.199%), followed by those exposed to immunosuppressant alone (0.012%), corticosteroid alone (0.008%), and neither medication (0.001%) (P < .001). The greatest risk differences were noted between groups exposed to immunosuppressant and corticosteroid compared with neither (0.198%, 95% confidence interval [CI] 0.166%-0.230%) or immunosuppressant alone (0.188%, 95% CI 0.155%-0.221%). The greatest relative risks (RRs) were noted among those receiving immunosuppressant and corticosteroid compared with those exposed to neither (RR 122.5, 95% CI 100.9-148.8) or immunosuppressant alone (RR 16.5, 95% CI 7.3-37.4). Limitations: We could not confirm dose and duration of exposures. Conclusion: Incidence of pneumocystosis among patients exposed to immunosuppressants is very low. Prophylaxis for patients receiving combination immunosuppressant and corticosteroid therapy, the group at highest risk, might be warranted.