A recent Chinese study showed that the coronavirus could be transmitted through air conditioning systems.
According to a preliminary publication in the Emerging Infectious Diseases newsletter, a new coronavirus outbreak can be caused by air conditioning. Although these results are very worrying, some experts believe they should be treated with caution.
To reach this conclusion, Chinese researchers looked at a dinner that took place at a restaurant in Guangzhou (China) on 24 January. On that day, a 63-year-old woman from Wuhan, the birthplace of the Covid 19 epidemic, attended the event. A few days later, she tested positive for the virus. After that, nine other clients of the restaurant fell ill successively with the disease. For at least two more people who were not sitting at her table, this lady was the only known source of contamination.
Apparently she infected people in front of her and behind her, but not the waiters who touched her plate and cutlery. Conclusion: The contamination came from the air system in the restaurant, concluded the researchers. Air conditioning can promote the transfer of contaminated aerosols to the other tables through the airflow, say the researchers. Aerosols are drops that are small enough to float in the air and move freely.
Transmission from the air remains a debatable issue
However, this study has some limitations. For example, researchers did not conduct experiments simulating the air transmission, or serological studies on asymptomatic members of the Wuhan family or other guests to assess the risk of direct infection.
Therefore, several experts worldwide expressed reservations about these results. “We can see that there was less than one meter between the infected at table A and the customers at table B, but the droplets could go up to 1.50 meters”. As for the contaminated customers at table C, “it does not make sense” says Jean-Christophe Lucet, head of the department of hygiene and nosocomial infection control at the Bichat Hospital in Paris. In fact, the air conditioning above this table blows in the opposite direction of the suspected contamination, explains the expert.
On the 6th of April, Finnish researchers showed that a person who coughs spreads particles in the form of an aerosol. The study showed their spread and explained that it is not yet known whether they are sufficient in this form to transmit the coronavirus. Thus, although there is little evidence of how the virus could spread through the air, the researchers concluded by reaffirming the importance of distancing and wearing a mask to protect others from respiratory droplets.
Insufficient virus load
For example, “studies so far seem to indicate that the virus responsible for Covid-19 is mainly transmitted by contact with respiratory droplets and not by air,” says the World Health Organization (WHO) on its website.
“At the moment, the only thing that has been scientifically proven is that there is an aerosol effect in the bedroom of a sick patient,” explains Daniel Camus, infectious diseases specialist at the Institut Pasteur in Lille, western France. “It has not been proven that ventilation or air conditioning systems pose any particular danger. The virus load is probably insufficient,” he says.
Furthermore, properly applied ventilation allows aerosols containing the virus to be diluted and then extracted from the room: “Increased ventilation rates are also recommended to combat airborne diseases, provided these systems are used properly: without recirculation and by directing the flows from clean areas to potentially contaminated areas,” Le Figaro points out.
Beware of vacuum cleaners
If in the 1960s it was proven that legionnaire disease (a serious infection of the airways caused by breathing in an aerosol of water contaminated with legionella bacteria) could be transmitted in air conditioning systems, it was because “at that time, air circulated in contact with water to humidify it,” Jean-Christophe Lucet explained to Franceinfo. Since then, the circulation systems have been different,” he says.
However, this information must be taken into account when reopening restaurants, shops, and businesses. If in doubt, we will have to continue to try to maintain barrier measures (social distance, coughing and sneezing at the elbows, use of a disposable scarf) as much as possible and favor open spaces to spaces with air conditioning.
Finally, if you have air conditioning in your home, remember to clean the vents and to maintain the filters. Above all, be careful when using vacuum cleaners as they can generate an aerosol. A vacuum cleaner that passes through the house of a contaminated person can put the particles back in suspension.