Patients with psoriasis have an increased incidence of any infection and of severe and rare infections compared with the general population, according to a study published online April 5 in the British Journal of Dermatology .

Nikolai Loft, M.D., from Copenhagen University Hospital in Denmark, and colleagues examined the incidence and risk for severe and rare infections in Danish patients with psoriasis and the matched general population using data from the Danish National Patient Register between Jan. 1, 1997, and Dec. 31, 2018. Patients with psoriasis were matched for age and gender with general population controls in a 1:6 ratio (94,450 patients and 566,700 controls). Severe infections were those requiring treatment in a hospital setting, while rare infections included HIV, hepatitis B and C, and tuberculosis.

The researchers found that compared with controls, patients with any psoriasis had higher incidence rates per 100,000 person-years of exposure: 3,104.9 and 2,381.1 for any infection; 3,080.6 and 2,364.4 for severe infections; and 42.9 and 31.8 for rare infections, respectively. The incidence rates for severe or rare infections were higher for patients with severe psoriasis (3,847.7) compared with patients with mild psoriasis and controls.

"Factors that may explain the increased risk of infection include the altered immune environment in patients with psoriasis involving a network of leukocytes and pro-inflammatory cytokines in disease pathogenesis," the authors write. "Patients with severe psoriasis are defined by their eligibility for systemics, either conventional or biologic. Therefore, the increased risk may be a consequence of treatment and not the severity of psoriasis."

Several authors disclosed financial ties to pharmaceutical companies, including Novartis Pharma, which funded the study.

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