Floor Sampling of SARS-CoV-2 in Hospitals May Signal Impending COVID-19 Outbreaks

In a recent study, SARS-CoV-2 RNA detected on hospital floors in health care worker-only areas was found to strongly correlate with COVID-19 outbreaks within the facility.

This study builds on prior findings from long-term care facilities where environmental detection of SARS-CoV-2 on floors was linked to impending outbreaks. The researchers aimed to assess if similar environmental sampling in hospitals could serve as an early indicator of outbreak risk, thereby enhancing infection control and surveillance. By focusing on healthcare worker-only areas—such as staff locker rooms—the study sought to determine if these zones, away from patient areas, could reflect SARS-CoV-2 presence indicative of wider viral spread in the hospital.

Over a 39-week period, weekly floor swabs were collected from staff areas in two Ontario hospitals. Swabs were tested using quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) to measure the SARS-CoV-2 viral load. To evaluate the association between floor viral burden and outbreak risk, the researchers used grouped fivefold cross-validation and measured model discrimination with the area under the receiver operating characteristic (AUC) curve.

The researchers found that 71% of 760 samples tested positive for SARS-CoV-2 RNA. Hospital A demonstrated a particularly high positivity rate of 90% (95% CI, 85%-93%; n = 280), compared to 60% (95% CI, 55%-64%; n = 480) at Hospital B. During the study period, Hospital A experienced four COVID-19 outbreaks, while Hospital B had seven, with a combined total of 140 patient cases and only four staff cases. The researchers observed that for every 10-fold increase in viral copies on floors, the odds of a COVID-19 outbreak increased 22-fold (OR = 22.0; 95% CI, 7.3-91.8). The model achieved strong predictive performance, with a cross-validated AUC of 0.86 (95% CI, 0.82-0.90), suggesting that floor SARS-CoV-2 levels could reliably indicate outbreak potential.

Study limitations include the focus on only two hospitals, and the lack of data on floor contamination sources, which might have provided additional context for infection control measures.

“Viral burden of SARS-CoV-2 on floors, even in healthcare worker-only areas, was strongly associated with COVID-19 outbreaks in those hospital wards,” the study authors concluded. “Built environment sampling may support hospital COVID-19 outbreak identification, fill gaps in traditional surveillance, and guide infection prevention and control measures.”

Reference

Fralick M, Moggridge JA, Wiebe M, et al. SARS-CoV-2 burden on the floor was associated with COVID-19 cases and outbreaks in two acute care hospitals. Infect Control Hosp Epidemiol. 2024;1-5.doi:10.1017/ice.2024.121