india

Updated: Apr 30, 2020 06:10 IST

Scientists in China have found genetic fragments of the virus that causes coronavirus disease (Covid-19) in airborne droplets in medical and staff areas during the outbreak in February and March in two Wuhan hospitals, but they stopped short of saying the disease is airborne.

An important finding of the study was that ventilation and sterilisation brought down airborne genetic shards (RNA) of Sars-CoV-2, the virus that causes Covid-19, to undetectable levels and reduced the risk of airborne exposure.

Small droplets expelled while breathing or talking can remain airborne and infect people who inhale them, said the study, but it could not determine whether the Sars-CoV-2 RNA were harmless or infectious. The study was published in the journal, Nature.

“Although we have not established the infectivity of the virus detected in these hospital areas, we propose that SARS-CoV-2 may have the potential to be transmitted via aerosols,” concluded the study that did an aerodynamic analysis of Sars-CoV-2 in two Wuhan hospitals.

“Viral RNA of positive strand is theoretically infectious but there are no known cases to my knowledge of RNA-mediated infection. Thus, practically, only intact virus/virion is infectious. Many of these studies that look at viral RNA should be interpreted with caution,” said Dr Anurag Agrawal, director, Institute of Genomics and Integrative Biology, New Delhi.

“Viral RNA is not infective,” said Soumya Swaminathan, chief scientist, World Health Organization (WHO), Geneva.

Covid-19 spreads primarily from person to person through small droplets from the nose or mouth, which are expelled when an infected person coughs, sneezes, or speaks, according to the WHO. These droplets are relatively heavy and quickly sink to the ground, but people can get infected if they inhale droplets from a sick person or touch contaminated objects and surfaces, then touching their eyes, nose or mouth, said the global health agency.

Earlier this month, a high-level US scientific panel said that the virus that causes the disease is airborne and can spread through just breathing and talking, which makes its spread easier and sustainable. The scientists from the US National Academies of Sciences, Engineering, and Medicine said the virus can stay suspended in air in the ultrafine mist that is produced when people exhale.

On March 17, a study published in the New England Journal of Medicine found the virus stayed suspended and infective in aerosol droplets that are below 5 microns across for up to three hours in lab conditions. The aerosolized virus had a median half-life of about 1.1-1.2 hours, similar to the related Sars-CoV, the coronavirus that causes Severe Acute Respiratory Syndrome (Sars), the study found. The half-life indicates how long a virus can survive in different environments, regardless of how much virus happens to be present at the time of sampling.

Infected people, who are asymptomatic or have mild symptoms of fever, cough or fatigue, also spread the disease to others, with a study from China published in Nature Medicine on April 15 estimating that 44% of infections are spread by people who are not obviously ill.

The study from China found that the concentration of Sars-CoV-2 RNA in aerosols detected in isolation wards and ventilated patient rooms was very low, but it was elevated in the patients’ toilet areas, indicating that they need the same level of sanitisation as the intensive care units and isolation wards.

“Levels of airborne Sars-CoV-2 RNA in the majority of public areas were undetectable except in two areas prone to crowding, possibly due to infected carriers in the crowd,” said the study, which also found high concentrations of viral RNA with aerosol size distributions in some medical staff areas.

The viral RNA, however, reduced substantially to undetectable levels after implementation of rigorous sanitisation procedures. “Our results indicate that room ventilation, open space, sanitisation of protective apparel, and proper use and disinfection of toilet areas can effectively limit the concentration of Sars-CoV-2 RNA in aerosols. Future work should explore the infectivity of aerosolized virus,” the study said.

It recommended that for public health prevention and medical staff protection, hospitals must focus on ventilation and sterilisation of toilets as a potential spread source of the virus; personal protection measures for the general public, such as wearing masks and avoiding crowded placed to reduce the risk of airborne virus exposure; and the effective sanitisation of the high risk area in the hospital to limit the transmission of airborne Sars-CoV-2 and protect the medical staff.

It highlighted that conversion of a naturally ventilated stadium into a field hospital for patient quarantine and treatment limited aerosol transmission of Sars-CoV-2; as did surface sanitisation of the personnel protection equipment before they are taken off, which reduced the potential infection risk of medical staff.