Dubai: As the world counts COVID-19 deaths and tallies up confirmed cases, researchers are trying to fill in all the gaps in information available on the novel coronavirus - SARS-CoV-2. The disease spreads through droplet transmission, but studies are ongoing on what can halt or aid this transmission despite social distancing and properr disinfection.
The early version of a recent Chinese study looks at the possibility of transmission aided by air-conditioning systems in enclosed spaces. The report published by CDC takes into account 10 cases in three families. The only common venue of probable contact of the three families (referred to as A, B and C by the researchers) before being diagnosed as positive for coronavirus was at a restaurant.
One of the families (A) had just traveled from Wuhan, Hubei Province, China. Patient one, in this case from family A, had lunch with the family a day after their return at a restaurant. On the same day, families B and C were also diners at the same restaurant, overlapping in time with family A. The tables were further than 1 metre in distance from each other, effectively fulfilling the 'physical distance' rule.
The only positive case at that point was patient one in family A, who started showing symptoms later that day. The researchers found that this patient was the source of transmission for at least one member of families B and C. The rest of the cases in each family was determined to be within-family transmissions.
The restaurant in this case was closed 5-storey building with no windows. Each floor had its own air-con system. The families dined on the third floor. All other diners on the floor were monitored and quarantined but no one else tested positive for COVID-19.
The research report said: "We conclude that in this outbreak, droplet transmission was prompted by air-conditioned ventilation. The key factor for infection was the direction of the airflow."
The study found that though virus droplets of small sizes can linger in the air and travel distances further than 1 metre, this particular case was not due to aerosol transmission and was not airborne. This was determined as no one else in the restaurant was infected and samples from the air conditioner tested negative.
The authors believe that while large virus-laden droplets cannot travel further than 1 metre, the strong airflow could have helped to propogate the droplets to the tables where families B and C dined.
The authors recommend "strengthening temperature-monitoring surveillance, increasing the distance between tables, and improving ventilation."
For a report by The Print, Sambuddha Chaudhuri, an epidemiologist at the Indian Institute of Technology, Bombay said “This virus is not airborne in the same way as viruses that cause common cold and flu. It is just that if a person sneezes, a thick spray gets created — that is when a virus is in the air. But it does not float around in the air — it settles on surfaces and can stay there for a very long time,” He added, "Having said that, in places like centrally air-conditioned shopping centres etc, where there are usually a lot of people, the virus can get recycled in the air for a short span of time."
WHO also mentions in its advisory for airborne diseases: "In health facilities where there is a high concentration of infectious patients, evidence shows that poorly ventilated buildings have higher risks of infectious disease transmission for patients, workers, and visitors."
What are others saying?
Studies so far, referenced by a USA Today article, indicate that theSARS-CoV-2 is active longest on glass (for up to 96 hours) and plastic or stainless steel surfaces (for up to 72 hours). The shortest time of survival of the virus was in aerosol form (as droplets in air) for up to four hours and on copper surfaces (4 hours) as copper is a natural virucide.
Therefore, while the virus can be airborne, it is understood to not be able to travel far or survive long in aerosol form. However, air-conditioning systems could aid in transmission given certain conditions such as airflow, improper filters, lack of ventilation etc. based on various studies.
This particular report, published on mSystems, studies other coronaviruses such as SARS and MERS as well as SARS-CoV-2. The study was done by experts in health, the built environment and microbiology from the University of Oregon and the University of California, Davis.
"Open a window"
They recommended that buildings with air delivery systems should take care not to recirculate indoor air which "could potentially increase the transmission potential." The experts added: "Even though viral particles are too small to be contained by even the best HEPA and MERV filters, ventilation precautions can be taken to ensure the minimization of SARS-CoV-2 spread."
These experts, just as in the Chinese study, call for better ventilation, along with bringing more air from outside in (rather than recirculating indoor air) and maintaining filters properly.
The experts add that the simple act of opening a window can also help, while being cautious about sudden temperature changes. They said, "the easiest way to deliver outside air directly across the building envelope is to open a window."
The California study also found that natural daylight could mitigate some risks. They determined this in a simulation where daylight exposure reduced the average half-life of exposed influenza virus from over 31 minutes to just over 2 minutes.