Updated: July 10, 2020 3:33:07 pm
The World Health Organisation (WHO) has admitted the possibility of airborne transmission of SARS-COV-2 during certain medical procedures and in crowded indoor settings with poor ventilation through aerosols — smaller airborne particles that linger in the air for longer periods of time.
“Airborne transmission of the virus can occur in health care settings where specific medical procedures, called aerosol generating procedures, generate very small droplets called aerosols. Some outbreak reports related to indoor crowded spaces have suggested the possibility of aerosol transmission, combined with droplet transmission, for example, during choir practice, in restaurants or in fitness classes,” the WHO said about the spread of the novel coronavirus Thursday.
Some #COVID19 outbreak reports related to crowded indoor spaces have suggested the possibility of aerosol transmission combined with droplet transmission e.g. during choir practice, in restaurants or gyms.
We need more studies to understand such outbreaks https://t.co/WHHe4vuyF8 pic.twitter.com/coWuRrLy5V
— World Health Organization (WHO) (@WHO) July 9, 2020
Airborne transmission is defined as the spread of an infectious agent caused by the dissemination of droplet nuclei or aerosols that remain infectious when suspended in air over long distances and time. Aerosols are less than 5 micrometers or five-thousandth of a millimetre in size.
In the absence of aerosol-generating procedures, the WHO has been evaluating whether the virus can spread through aerosols. The virus is primarily transmitted between people via respiratory droplets and contact routes, the agency maintained.
“However, the proportion of exhaled droplet nuclei or of respiratory droplets that evaporate to generate aerosols, and the infectious dose of viable SARS-CoV-2 required to cause infection in another person are not known, but it has been studied for other respiratory viruses,” the organisation said.
“Some studies conducted in health care settings where symptomatic COVID-19 patients were cared for, but where aerosol generating procedures were not performed, reported the presence of SARS-CoV-2 RNA in air samples (23-28), while other similar investigations in both health care and non-health care settings found no presence of SARS-CoV-2 RNA,” it added.
It also noted that close contact environments of crowded indoor spaces may have perhaps facilitated the transmission of the virus from a small number of cases to many other people in cases where masks were not used.
“Recent clinical reports of health workers exposed to Covid-19 index cases, not in the presence of aerosol-generating procedures, found no nosocomial transmission when contact and droplet precautions were appropriately used, including the wearing of medical masks as a component of the personal protective equipment (PPE),” WHO said.
It added: “These observations suggest that aerosol transmission did not occur in this context. Further studies are needed to determine whether it is possible to detect viable SARS-CoV-2 in air samples from settings where no procedures that generate aerosols are performed and what role aerosols might play in transmission.”
Meanwhile, the role of blood-borne transmission of SARS-COV-2 remains uncertain.
“Currently, there is no evidence for intrauterine transmission of SARS-CoV-2 from infected pregnant women to their fetuses, although data remain limited,” WHO has said, adding that low viral titters in plasma and serum also suggested that risk of blood-borne transmission may be low.
Fomite transmission is considered a likely mode of transmission for the virus.
“Respiratory secretions or droplets expelled by infected individuals can contaminate surfaces and objects, creating fomites (contaminated surfaces). Viable SARS-CoV-2 virus and/or RNA detected by RT-PCR can be found on those surfaces for periods ranging from hours to days, depending on the ambient environment (including temperature and humidity) and the type of surface, in particular at high concentration in health care facilities where Covid-19 patients were being treated. Therefore, transmission may also occur indirectly through touching surfaces in the immediate environment or objects contaminated with virus from an infected person (e.g. stethoscope or thermometer), followed by touching the mouth, nose, or eyes,” it observed.
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