The environmental surveillance of surface contamination is a new tool for understanding the transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes the coronavirus disease (COVID-19).
Though the primary mode of transmission of SARS-CoV-2 is through respiratory droplets, and in some instances, aerosols, it is vital to understand if high touch non-porous surfaces pose a risk of virus spread.
A team of researchers at Tufts University found that 8.3 percent of surface samples tested positive for SARS-CoV-2, including crosswalk buttons, trash can handles, and door handles of essential business entrances such as grocery stores, banks, gas stations, and liquor stores.
Contamination of surfaces
SARS-CoV-2 is believed to be primarily transmitted through droplets and aerosols. Yet, the role of fomites in the transmission is still unclear. Though some studies have noted that the risk of virus spread via fomites may be low in clinical settings, the World Health Organization (WHO) says that fomites may contribute to the spread of COVID-19.
The U.S. Centers for Disease Control and Prevention (CDC) also noted that contact transmission is spread through direct contact with an infected person or with an article or surface that has been contaminated, referred to as fomite transmission.
As the pandemic evolved over the last months, scientists have detected SARS-CoV-2 in various objects, including wastewater and surfaces in both clinical settings and community locations. However, SARS-CoV-2 detection in high-touch surfaces and essential businesses is limited.
Environmental surveillance plays a pivotal role in determining the virus's presence on surfaces, which may heighten the risk of infection. Surveillance of environmental reservoirs has been a less invasive and low-cost method to detect the virus.
The study, published on the preprint server medRxiv*, highlights the risk of fomites in the spread of SARS-CoV-2, the virus that causes COVID-19.
To arrive at the study findings, the researchers collected high-touch surface samples in public areas and essential businesses throughout a COVID-19 outbreak between March and June 2020 in Somerville, Massachusetts.
The team aimed to document the types of high-touch non-porous surfaces likely to be contaminated with the coronavirus, measure the concentration of SARS-CoV-2 on surfaces, and evaluate the link between environmental surface SARS-CoV-2 contamination levels and COVID-19 cases in the community.
The researchers collected surface swab samples and recorded touches on 33 unique surfaces at 12 locations, including a trash can, liquor store, bank, grocery store, metro entrance, gas station, restaurant, laundromat, convenience store, crosswalks, and post office boxes. They measure the SARS-CoV-2 RNA in surface swab samples by real-time quantitative reverse transcription-polymerase chain reaction (RT-qPCR).
Of the 347 total surface samples, 29 or 8.3 percent tested positive for the virus RNA, and the team detected SARS-CoV-2 on surfaces in 10 out of 12 locations sampled. Of all the surfaces, 17 or 52 percent were positive for SARS-CoV-2 at least once. Further, the virus was detected on surfaces at all locations except for the post office box and convenience store.
The most frequently contaminated surfaces include trash can holders, bank door handles, and liquor store door handles.
The study findings show that the prevalence of SARS-CoV-2 RNA on high-touch surfaces in public areas and essential businesses reflected local COVID-19 case numbers one week. Further, the findings underline the potential for environmental surveillance of high-touch surfaces to inform disease dynamics during a pandemic.
The team added that high-touch surface monitoring could be useful at finer spatial spaces such as within buildings when mass testing is not possible. Surface sampling could provide insight into potential areas where there are positive cases. Also, testing surfaces may detect potential positive cases since most infected people are asymptomatic or pre-symptomatic.
"Our findings contribute to a growing literature of detectable but low-level SARS-CoV-2contamination on public surfaces," the team wrote in the study.
"Estimated risk of infection from exposure to the contaminated surfaces here is lower than estimates for inhalation exposure to SARS-CoV-2, and lower than fomite transmission risk of other respiratory pathogens," they added.
Overall, the study results are consistent with the current consensus that fomite transmission of SARS-CoV-2 is possible, but it is likely a secondary pathway.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.