COVID on the Floor Linked to Outbreaks on Two Hospital Wards

The viral burden of SARS-CoV-2 on floors, even in healthcare worker–only areas, was strongly associated with COVID-19 outbreaks in two acute-care hospitals, according to a new study from Ontario, Canada.

With every 10-fold increase in viral copies, the chance of an impending outbreak of COVID-19 rose 22-fold. The results suggest that frequent floor sampling could play an important role in a more localized surveillance of the virus, the authors wrote.

“These data add to the mounting evidence that built environment detection for SARS-CoV-2 may provide an additional layer of monitoring and could help inform local infection prevention and control measures,” they wrote.

The study was published online on September 20 in Infection Control & Hospital Epidemiology. 

Preventing Future Suffering 

The current study builds on the researchers’ previous work, which found the same correlation between viral load on floors and COVID outbreaks in long-term care homes. 

Currently, the best-known method of environmental surveillance for COVID is wastewater detection. “Swabbing the floors would be another approach to surveillance,” senior author Caroline Nott, MD, infectious disease physician at the Ottawa Hospital, told Medscape Medical News. 

“We do have environmental surveillance with wastewater, but while this may tell you what’s going on in the city, it doesn’t tell you what is going on in a particular ward of a hospital, for instance,” she added. 

Nott and her colleagues believe that swabbing, which is easy and relatively inexpensive, will become another tool to examine the built environment. “Instead of having to close a whole hospital, for example, we could just close one room instead of an entire ward if swabbing showed a high concentration of COVID,” Nott said. 

The current study was conducted at two hospitals in Ontario between July 2022 and March 2023. The floors of healthcare worker–only areas on four inpatient adult wards were swabbed. These areas included changing rooms, meeting rooms, staff washrooms, nursing stations, and interdisciplinary team rooms.

SARS-CoV-2 RNA was detected on 537 of 760 floor swabs (71%). The overall positivity rate in the first hospital was 90% (n = 280). In the second hospital, the rate was 60% (n = 480).

Four COVID-19 outbreaks occurred in the first acute care hospital, and seven outbreaks occurred at the second hospital. Outbreaks occurred mostly among hospitalized patients (140 cases), but also in four hospital workers.

COVID-19 still requires vigilance, said Nott. “We weren’t prepared for COVID, and so as a result, many people died or have suffered long-term effects, especially vulnerable people like those being treated in hospital or in long-term care facilities. We want to develop methods to prevent similar suffering in the future, whether it’s a new COVID variant or a different pathogen altogether.” 

Changing Surveillance Practice?

“This is a good study,” Steven Rogak, PhD, professor of mechanical engineering at the University of British Columbia (UBC) in Vancouver, told Medscape Medical News. “The fundamental idea is that respiratory droplets and aerosols will deposit on the floor, and polymerase chain reaction [PCR] tests of swabs will provide a surrogate measurement of what might have been inhaled. There are solid statistics that it worked for the hospitals studied,” said Rogak, who studies aerosols at UBC’s Energy and Aerosols Laboratory. Rogak did not participate in the study. 

“The authors note several limitations, including that increased healthcare worker testing may have been triggered by the higher values of PCR counts from the floor swabs. But this doesn’t seem to be a problem to me, because if the floor swabs motivate the hospital to test workers more, and that results in identifying outbreaks sooner, then great,” he said.

“Another limitation is that if the hospital has better HVAC or uses air purifiers, it could remove the most infectious aerosols, but the large droplets that fall quickly to the ground would remain, and this would still result in high PCR counts from floor swabs. In this case, perhaps the floor swabs would be a poorer indication of impending outbreaks,” said Rogak.

Determining the best timing and location for floor swabbing might be challenging and specific to the particular hospital, he added. ”For example, you would not want to take swabs from floors right after they are cleaned. Overall, I think this method deserves further development, and it could become a standard technique, but the details might require refinement for widespread application,” he said.

Adrian Popp, MD, chair of the Infectious Disease Service at Huntington Hospital-Northwell Health in Huntington, New York, said that although interesting, the study would not change his current practice.

“I’m going to start testing the environment in different rooms in the hospital, and yes, I might find different amounts of COVID, but what does that mean? If pieces of RNA from COVID are on the floor, the likelihood is that they’re not infectious,” Popp told Medscape Medical News.

“Hospital workers do get sick with COVID, and sometimes they are asymptomatic and come to work. Patients may come into the hospital for another reason and be sick with COVID. There are many ways people who work in the hospital, as well as the patients, can get COVID. To me, it means that in that hospital and community there is a lot of COVID, but I can’t tell if there is causation here. Who is giving COVID to whom? What am I supposed to do with the information?” 

The study was supported by the Northern Ontario Academic Medicine Association Clinical Innovation Opportunities Fund, the Ottawa Hospital Academic Medical Organization Innovation Fund, and a Canadian Institutes of Health Research Operating Grant. One author was a consultant for ProofDx, a startup company creating a point-of-care diagnostic test for COVID-19, and is an advisor for SIGNAL1, a startup company deploying machine-learning models to improve inpatient care. Nott, Rogak, and Popp reported having no relevant financial relationships.