Background: Immunosuppressants lead to an increased risk of infection, but few prospective studies have assessed the incidence of opportunistic infections in inflammatory bowel disease (IBD) patients, a high proportion of whom are treated with immunosuppressants. The aim of this study was to assess the age distribution of Japanese IBD patients with opportunistic infections and the risk factors associated with these infections. Methods: A multicenter, prospective study of 570 IBD patients was conducted. The patients were followed for up to 12 months to identify any new infections. The incidence of opportunistic infections and the age distribution of patients with these infections were analyzed. We carried out a case-control study in which 2 non-infected IBD patients were selected as controls for each case (infected IBD patient); the effect of medications on the infection rate was also examined. Results: Fifty-two (9.1 %) of 570 IBD patients developed opportunistic infections. Herpes simplex virus and herpes zoster virus infections were observed in 29 and 16 patients, respectively. No cases of active tuberculosis were observed. The incidence of opportunistic infections in patients aged 50 years or over was significantly higher than that in the other age groups (p = 0.01). The use of steroids (p = 0.02), thiopurine (p < 0.01), and immunosuppressant combination therapy (p < 0.01) was associated with an increased rate of opportunistic infections. However, the use of infliximab was not associated with an increased rate of opportunistic infections (p = 0.62). Multivariate analysis indicated that the use of thiopurine was an independent risk factor for opportunistic infections (p < 0.01). Conclusions: Age ≥50 years and the use of immunosuppressants are risk factors for opportunistic infections in patients with IBD. In our cohort, tuberculosis was not seen as a complication of immunosuppressant therapy.
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