Background Understanding patterns of environmental contamination by SARS-CoV-2 is essential for infection prevention policies. Methods We screened surfaces and air samples from single bed ICU rooms of COVID-19 adult patients for SARS-CoV-2 RNA and viable viruses. Results and discussion We evidenced viral RNA environmental contamination in 76% of 100 surfaces samples and in 30% of 40 air samples without any viable virus detection by cell culture assays. No significant differences of viral RNA levels on surfaces and in ambient air were observed between rooms of patients with assisted mechanical ventilation and those of patients with high-flow nasal cannula system. Using an original experimental SARS-CoV-2 infection model of surfaces, we assessed that infectious viruses might have been present on benches within 15 hours before the time of sampling in patient rooms. Conclusions We observed that SARS-CoV-2 environmental contamination around COVID-19 patients hospitalized in single ICU rooms was extensive and that a high-flow nasal cannula system did not generate more viral aerosolization than a mechanical ventilation system in COVID-19 patients. Despite an absence of SARS-CoV-2 viable particles in study samples, our experimental model confirmed the need to apply strict environmental disinfection procedures and classical standard and droplet precautions in ICU wards.