'Airborne transmission of Coronavirus is possible'

A new CSIR-CCMB study reveals that viral particles were detected in the air, especially in closed rooms and hospitals where COVID-19 positive individuals had spent longer periods

When the Coronavirus pandemic spread across the world last year, the World Health Organisation (WHO) said that the SARS-CoV-2 (the virus that causes COVID-19) spreads primarily through small droplets expelled from the nose and mouth of an infected person that quickly sink to the ground. More and more research, however, emerged hinting at the possibility of airborne transmission of the virus. In an open letter to the WHO, published in the Clinical Infectious Diseases journal, 239 scientists in 32 countries outlined evidence that they say shows that floating virus particles can infect people who inhale them. Finally, in July 2020, the WHO had to acknowledge the different studies and reports.

This set in motion a new study in September 2020 by the CSIR-Centre for Cellular & Molecular Biology (CCMB) in India. CCMB director Rakesh Mishra says, “When a lot of significant data emerged about how the virus from an infected person can spread through air, we initiated this study. The question we had in our minds was—if it can travel through air, how long does it stay there for? How long can it spread? We wanted answers to these questions so that our government can come up with new guidelines to protect people from getting infected.”

The study has been published in the preprint server medRxiv. The team analysed the air samples collected from various enclosures in hospitals in Hyderabad and Mohali, Punjab. “We collected 64 air samples from COVID-19 and non-COVID areas of various hospitals and 17 samples from closed rooms occupied by COVID-19 patients. Four samples from COVID care areas were positive for SARS-CoV-2 with no obvious predilection towards ICU/non-ICU areas in the hospital samples. In the closed room experiments, where one or more COVID-19 patients spent a short duration of time, one sample—collected immediately after the departure of three symptomatic patients from the room—was positive. Our results indicate that the chance of picking up SARS-CoV-2 in the air is directly related to the number of COVID-19 positive cases in the room,” mentions Mishra in the report.

Rakesh Mishra

While taking air samples for a certain period of time was not a herculean task, recovering viral material and bringing it to the laboratory for testing was crucial. “We used air samplers for this. The viral material was collected inside the filter, which was then opened in the laboratory to study it. This was the most significant part of the research,” he says.

The study, which is yet to be peer-reviewed, also revealed that when COVID-19 patients spent long hours in a room, the virus was found in the air for more than two hours. However, for asymptomatic cases, they showed the virus does not spread farther from them when they are seated in a room without perceived airflow due to a fan or AC. “All these findings show that the virus can stay in the air for some time. Detecting and isolating the positive cases early can help prevent the spread among other family members in a home setting, too. For instance, people tend to not wear masks in their homes. But if an infected person is in home quarantine, other members of the family need to continue wearing masks,” Mishra adds.

The principal mode by which people are infected with SARS-CoV-2 is through exposure to respiratory droplets carrying the infectious virus. Respiratory droplets are produced while breathing, speaking, singing, coughing, sneezing, and are divided into two basic categories based on how long they can remain suspended in the air: Larger droplets, some of which are visible, and smaller droplets and particles (formed when small droplets dry very quickly in the airstream) that can remain suspended for many minutes to hours and travel far from the source on air currents. “Multiple papers, along with ours, are coming up with similar findings. Until now, nobody was talking about or had conducted air surveillance on COVID-19,” Mishra informs.

He also stresses on the fact that caution needs to be exercised while using both public and home toilets as flushing has the potential to generate aerosols, which can stay longer in the air. This is important because the virus is known to be excreted in stool. “Nobody tends to wear a mask when they go to the loo. But toilets are closed rooms, where there is little or no ventilation. And therefore, if an infected person has used the toilet before you, there are chances that the virus has stayed there. You may take off your mask thinking you are alone, but the virus is present with you,” he warns.

These findings have significant implications in the current situation, when many countries have relaxed the restrictions on public mobility and interactions, even when the number of COVID-19 cases is increasing steadily. “In many densely populated nations, where the recommended physical distancing norms may be difficult to implement in public/office spaces, distancing as much as possible with usage of masks should be actively promoted. Whilst, any form of verbal communication from closed quarters without wearing masks should be prohibited,” the study concludes.

The team now plans on conducting a larger research in public settings like malls, theatres, public toilets, etc., to understand how this will impact large gatherings.

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