Environmental surveillance for SARS-CoV-2 for outbreak detection in hospital: A single centre prospective study

Identifying COVID-19 outbreaks in hospitals at an early stage requires active surveillance. Our objective was to assess whether floor swabs correlated with COVID-19 outbreak status in hospital. We swabbed the floors of an inpatient ward at Mount Sinai Hospital for 32 weeks, from October 31, 2022 to June 15, 2023 and RT-qPCR analysis provided a quantification cycle of detection for each positive swab. 182 swabs were processed for SARS CoV-2, of which 98.4% were positive. Two COVID-19 outbreaks were declared during the study period. The median viral copy number was 210 (IQR, 49 to 1018) during non-outbreak periods and 653 (IQR, 300 to 1754) during outbreak periods. Analyzing the number of viral copies of SARS-CoV-2, instead of percentage positivity, gave a clearer view of changes in outbreak status over time, thereby illustrating the benefits of this approach to monitor pathogen load in hospital settings.