A new study by laboratories in Hyderabad and Mohali has found fresh evidence that the risk of airborne transmission of the novel coronavirus is quite low if sufficient physical distance is maintained and prolonged interaction with an infected person is avoided.
The transmission of SARS-CoV2 was initially thought to be happening mainly through contact and droplets coming out during speech, coughs or sneezes. But several studies later reported transmission among people who were suitably distanced but had shared enclosed spaces, like a closed room or vehicle. That suggested that the virus possibly travels in air to far greater distances than the two to three feet that was originally considered the zone of risk.
Scientists at two laboratories of the Centre of Scientific & Industrial Research (CSIR), the Centre for Cellular and Molecular Biology in Hyderabad, and Institute of Microbial Technology in Chandigarh, have studied the extent of transmission through air. The study, conducted in hospitals in these two cities, found that the risk of exposure in closed rooms through airborne transmission was higher if there were more infected people present, but that in normal circumstances the virus was not found more than four feet from the infected person. The study has said that demarcating Covid and non-Covid areas in hospitals was a good strategy, and that masks were still very effective.
“Not that we did not know these things, but we have been able to generate more data which validate it from a scientific perspective,” said Shekhar Mande, Director General of CSIR.
Sampling & findings
The scientists collected 64 air samples from different locations in six hospitals in these cities, and another 17 from closed rooms occupied by infected people who were without masks and asked to talk on the phone or with one another. Four samples taken from Covid areas of hospitals, and one from the closed room were found to contain the virus.
“The virus could not be detected in any of the non-Covid areas, providing objective evidence that the strategy of separating hospital premises into Covid and non-Covid care areas is effective,” said the study, which is currently on a preprint server.
“The positivity rate was found to be higher when the number of COVID patients were higher in the room… A point to be highlighted from the hospital experiments was that in three-fourth of the samples which were positive, the sampler was at least 10 feet away from the nearest patient… this may be an indicator that long term presence of COVID positive patients in an enclosed space may contribute to a significant increase in aerosol burden in the air,” the study said.
The study also found that in “neutral” conditions, with no particular air flow direction, the virus did not travel much in the air.
“Virus could not be picked up at a distance of even 4 feet when COVID positive individuals spent a short time (20 minutes) in the room. This indicates that short duration of exposure to a COVID positive individual may not put one at a significantly increased risk. The samples collected at 8 feet and 12 feet subsequently were also negative,” it said.
Takeaways & recommendations
Based on this study, and also the findings from some other studies, the CSIR has issued an advisory
PUBLIC TRANSPORT: Exposure to a Covid-19-positive individual for a short duration (30 minutes) when adequate precautions are being taken does not significantly increase the risk of contracting the disease. Taking this into consideration, short-duration travel in Metro/local trains or buses is likely to be safe. If one needs to travel longer, the journey may be broken in to parts to mitigate the risk. For example, if the journey from point A to B is for an hour, it can be broken down in to two journeys of half an hour each.
CAUTION ON PUBLIC TOILETS: Flushing has the potential to generate aerosols which can stay longer in the air and the virus is known to be excreted in stool. Masks should be always kept on while using these and if possible, the same toilet should be reused only half an hour after the previous use. Pictorial instructions should be stuck in the toilets regarding cleaning them after utility. This should be followed by adequate hand hygiene.
HOME & HOSPITAL: Spending more time in closed spaces can be risky even if social distancing is maintained. Open, well-ventilated spaces carry less risk of infection. In a family, if a person tests Covid-19-positive and is advised by the doctor to be home-quarantined, he/ she should be isolated in a separate room to prevent the infection spreading to other family members. His/her toilet should be separate from the toilet(s) used by others.