Researchers isolate live coronavirus from hospital air samples, warn aerosols may serve as a source of spread
There is substantial debate about the role played by the coronavirus in aerosols or floating respiratory droplets in disease transmission. The World Health Organization (WHO) recently issued guidelines that said that the airborne spread of Covid-19 may be possible in indoor settings but called for more evidence. A research team has now succeeded in isolating live coronavirus from air samples that were collected at a distance of 2 to 4.8 meters (about 6.5 feet to about 15.7 feet) from Covid-19 patients in a US hospital. Current social or physical distancing guidelines issued by the US Centers for Disease Control and Prevention (CDC) recommends keeping at least 6 feet away from other people.
The scientists showed that the virus isolated from air samples could infect cells in a lab dish. The findings reveal that viable SARS-CoV-2, the virus that causes Covid-19, can be present in aerosols generated by a coronavirus patient in a hospital room in the absence of an aerosol-generating procedure and can thus serve as a source for transmission of the virus, concludes the team from the University of Florida.
“Airborne SARS-CoV-2 was present in a location with Covid-19 patients. The distance from the air-samplers to the patients (2 meters and above) suggests that the virus was present in aerosols. Unlike previous studies, we have demonstrated the virus in aerosols can be viable, and this suggests that there is an inhalation risk for acquiring Covid-19 within the vicinity of people who emit the virus through expirations, including coughs, sneezes and speaking,” write the authors in their study. The findings, published as a pre-print, are yet to be peer-reviewed.
Commenting on the study, Linsey Marr, an engineering professor at Virginia Tech with expertise in airborne transmission of viruses, air quality, and nanotechnology, tweeted: “If this isn't a smoking gun, then I don't know what is.”
The WHO defines airborne transmission as “the spread of an infectious agent caused by the dissemination of droplet nuclei (aerosols) that remain infectious when suspended in air over long distances and time.” According to the agency, Covid-19 is primarily spread through contact and respiratory droplets. Under some circumstances, the airborne transmission may occur -- such as when aerosol-generating procedures are conducted in healthcare settings or potentially, in indoor crowded poorly ventilated settings elsewhere, it says. The scientific brief issued by the WHO in July explains that there have been reported outbreaks of coronavirus in some closed settings, such as restaurants, nightclubs, places of worship or places of work where people maybe shouting, talking, or singing. In these outbreaks, aerosol transmission, particularly in these indoor locations where there are crowded and inadequately ventilated spaces where infected persons spend long periods with others, cannot be ruled out, says the WHO. The agency, however, emphasizes that more studies are urgently needed to investigate such instances and assess their significance for transmission of Covid-19.
(Getty Images)
In the current study, air samples were collected in the room of two Covid-19 patients. Since the researchers had previously collected SARS-CoV-2 from the air of a respiratory illness ward within a clinic but were unable to isolate the virus in cell cultures “due to out-competition by other respiratory viruses,” this time they sought to perform air sampling tests in a hospital room reserved for Covid-19 patients. The aim was to lessen the probability of collecting other airborne human respiratory viruses.
Air samplings were performed at the University of Florida Health (UF Health) Shands Hospital, which is a 1,050-bed teaching hospital situated in Gainesville, Florida. As of July 10, over 200 patients have been treated at the hospital for coronavirus. The current study was conducted as part of ongoing environmental investigations by the UF Health infection control group to assess possible healthcare worker exposure to coronavirus.
“Viable virus was isolated from air samples collected 2 to 4.8m away from the patients. The genome sequence of the SARS-CoV-2 strain isolated from the material collected by the air samplers was identical to that isolated from the nasopharyngeal swab from the patient with an active infection,” the findings state. It adds, “Patients with respiratory manifestations of Covid-19 produce aerosols in the absence of aerosol-generating procedures that contain viable SARS-CoV-2, and these aerosols may serve as a source of transmission of the virus.”
The authors emphasize that scientific information on the mode of transmission should guide current best practices for limiting the spread of Covid-19. The public health implications of the current analysis are broad, especially as current best practices for limiting the spread of coronavirus center on social distancing, wearing of face-coverings while in proximity to others and hand-washing, they add. The report warns that for aerosol-based transmission, measures such as physical distancing by 6 feet would not be helpful in an indoor setting and would provide a false sense of security and lead to exposures and outbreaks. “With the current surges of cases, to help stem the Covid-19 pandemic, clear guidance on control measures against SARS-CoV-2 aerosols are needed,” says the team.