Risk of Serious Infection, Opportunistic Infection, and Herpes Zoster among Patients with Psoriasis in the United Kingdom

The risk of infection among patients with psoriasis of varying severity in a broadly representative population remains poorly understood. Using The Health Improvement Network (THIN), an electronic medical records database representative of the general UK population, we performed a cohort study to determine the risks of serious infection, opportunistic infection, and herpes zoster among patients with versus without psoriasis and according to psoriasis severity. We identified 187,258 patients with mild and 12,442 patients with moderate to severe psoriasis based on treatment patterns. Using Cox proportional hazards regression, the adjusted hazard ratios (95% confidence intervals) for serious infection were 1.18 (1.16-1.21) and 1.63 (1.52-1.75) for the mild and moderate to severe psoriasis groups, respectively. Among a nested cohort of 8,569 psoriasis patients with disease severity classified by body surface area involvement, similar results were obtained with the exception of an attenuated but significantly increased risk of serious infection among the moderate to severe psoriasis group (1.27 [1.10-1.47]). Overall, the risks of opportunistic infection and herpes zoster were significantly increased only among the moderate to severe psoriasis group and were associated with immunosuppressive therapy. Our analyses suggest that psoriasis is associated with an increased risk of serious infection, and psoriasis severity is a predictor of serious infection risk.