Nosocomial COVID-19 infections are a challenge for hospitals. In order to assess possible demographic, personal, environmental or medical care related risk factors, data of nosocomial cases occurring in the Service of internal medicine at CHUV between February and March 2021 were retrospectively analyzed. Neither personal nor medical care related factors were identified as risk factor for a nosocomial infection. However, a significant number of patients with hospital-acquired COVID infection stayed in a 5-bed ward (versus 1-2 beds) and shared toilets in these rooms. Patient distancing measures and weekly screening led to a subsequent significant reduction of nosocomial SARS-CoV-2 infections.