Introduction:
The impact of pharmacological immunosuppression (IS) on COVID-19 outcomes is unclear. This study aimed at investigating the outcomes of hospitalised patients undergoing IS and focussed on length of hospital stay, admission to intensive care unit (ICU) and mortality.

Material and methods:
Patients admitted to public hospitals in Southern Switzerland with SARS-CoV-2 infection (n = 442) were prospectively included, and their data were collected and analysed. Immunosuppressed patients were compared to patients from the same cohort but without any IS.

Results:
Thirty-five patients (7.9%, 65.7% male, median age 70.6 years) were treated with IS at the time of hospital admission. Compared with patients without IS, immunosuppressed patients showed higher mortality (n = 16 / 35, 45.7% vs n = 95 / 407, 23.3% p = 0.003) and longer hospital stay (median = 15.5 days vs median = 11, p = 0.0144). Moreover, in the univariate and multivariable logistic regression analysis, IS was independently associated with mortality (OR = 2.76 (95%-CI: 1.37-5.59) and 2.66 -95%-CI: 1.19-5.94 -) and in the linear univariate and multivariable regression analysis with the length of stay (p = 0.005 and p = 0.007). Furthermore, patients under IS were more often admitted to the ICU, although the association was not significant (p = 0.069).

Conclusions:
Patients under IS were at a significantly higher risk of severe and prolonged COVID-19 disease, with higher mortality and more extended hospital stay than patients without IS.