Impact of environmental contamination by SARS-CoV-2 in residential dwellings

A team of scientists from the United States recently unveiled this environmental contamination of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in households by surface sampling. In addition, the results reveal that certain bacterial communities in surface samples can be used as predictors of positive or negative status of SARS-CoV-2.

The study is currently available on the medRxiv* preprint server, while the article is subject to peer review

Background

SARS-CoV-2, the causative agent of coronavirus disease 2019 (COVID-19), is a positive-sense enveloped single-stranded RNA virus that spreads primarily via respiratory droplets or aerosols. However, there is some evidence that viral transmission can occur via contaminated surfaces. In previous outbreaks other betacoronavirus, such as the Middle East respiratory syndrome coronavirus (MERS), several studies have been conducted to detect the presence, persistence and viability of the virus on surfaces and in the air. Assessment of environmental contamination is particularly useful for understanding the persistence of viable viruses on high contact surfaces in hospitals or isolation rooms that may actively participate in viral transmission.

In the present study, scientists evaluated the presence of SARS-CoV-2 on interior surfaces to understand the possibility of direct (contacting surfaces) or indirect (via droplets or aerosols) viral transmission.

Study design

To estimate viral loads on surfaces, scientists collected a total of 381 samples from three housing units where people with SARS-CoV-2 were living in isolation. They collected respiratory samples from each infected individual on the day of the surface sampling. All surface samples were tested for SARS-CoV-2 using reverse transcription-polymerase chain reaction (RT-PCR).

In addition, the scientists investigated whether there was an association between the positive or negative status of SARS-CoV-2 and the presence of bacterial communities in the samples tested.

Important Notes

Of 381 samples tested, 178 were positive for SARS-CoV-2 (47%). The positivity rates were comparable in two dwellings (53% and 61%); however, the third unit had a significantly lower positivity rate (24%). In all units tested, the viral detection rate was highest in the rooms. Likewise, the highest viral load was observed in frequently touched surfaces (switches and handles), followed by floors and heavy-duty objects (refrigerator, sink, toilet and bed). In objects with flat handles and surfaces, such as refrigerators, cabinets, and drawers, the detectable viral load was only seen on affected handles, but not on flat surfaces.

Analysis of the alpha diversity of bacteria in the samples tested revealed a statistically significant association with the positive / negative status of SARS-CoV-2. However, the results indicated that the presence of a bacterial community is not sufficient to predict SARS-CoV-2 status in a single sample.

Further analysis of the differentially abundant bacteria in the samples tested revealed that Rothia dentocariosa is positively associated with SARS-CoV-2 status. Rothia dentocariosa is a Gram-positive bacteria belonging to the normal microbial community located in the mouth and respiratory tract. In addition, some bacterial communities belonging to the genus Corynebacterium were identified as predictors of positive samples for SARS-CoV-2.

Importance of the study

The results of the study demonstrate the presence of SARS-CoV-2 and related bacterial communities on high contact surfaces of households with individuals infected with SARS-CoV-2. The study highlights the importance of surface sampling as a sensitive and inexpensive method for detecting environmental contamination with SARS-CoV-2 in residential dwellings.

Importantly, the study analyzed changes in bacterial communities in individuals infected with SARS-CoV-2 that can be detected in the indoor environment. In numerous surface samples obtained at various locations, Rothia dentocariosa has been identified as an independent predictor of positive status for SARS-CoV-2.

Although bacterial communities belonging to the genus Corynebacterium have been identified as predictors of SARS-CoV-2 status in surface samples, previous studies have shown that COVID-19 patients have a significantly lower level of Corynebacterium in the oral microbiome. In the current study, scientists hypothesize that the presence of Corynebacterium and SARS-CoV-2 in surface samples could be associated with skin contamination.

*Important Notice

medRxiv publishes preliminary scientific reports which are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.