Can air conditioners spread COVID-19?
In the warmer months, air conditioning is essential.
Is this a concern when it comes to the coronavirus's spread?
The response to that question is dependent on how the virus is transmitted, which is still under investigation.
The most popular method of transmission is droplet transmission: When an infected person breathes, speaks, coughs, or sneezes, a virus-filled molecule of breath or saliva comes out of their nose or mouth. Generally, these droplets disperse within a few feet of the individual who exhales them. They will, however, transmit the virus if they come into contact with someone's eyes, nose, or mouth.
Then, aerosol transmission occurs when a sick person exhales microscopic infectious particles that remain in the air and spread from person to person through air currents. Aerosols can fly longer distances and penetrate deeper into the lungs of someone who inhales them because they are much smaller than droplets.
The degree to which aerosol transmission causes the infection is a point of contention among scientists. However, it is widely acknowledged that it does occur, especially in enclosed indoor settings. As a result, air conditioning may be a possible mode of transmission, sucking in virus particles exhaled by an infected individual and then blowing those infectious particles back out in the same room or even a room many floors away.
In reality, other infectious diseases like measles, tuberculosis, chickenpox, influenza, smallpox, and SARS have all been linked to HVAC systems.
However, it isn't easy to draw firm conclusions about the position of HVAC systems in the spread of COVID-19. Some research studies have been published on the topic, and experts agree that further research into the role of HVAC systems in the spread of the novel coronavirus is needed.
"We didn't concentrate on ventilation as much as we possibly should have early on," says Abraar Karan, a Harvard Medical School physician, and global health researcher.
As mandated by building codes, HVAC systems carry in outside air and exhaust an equivalent amount of indoor air. This air exchange aims to dilute and eliminate pollutants such as particles, chemical pollution from building materials, and odor-causing emissions from people. Many devices recirculate indoor air, which could theoretically disperse viral aerosol particles from one space to another, but no evidence of COVID-19 infections has been found to date. As recirculated air passes through filters before being returned to conditioned rooms, it also helps to eliminate pollutants from the air.
Researchers in Oregon collected samples from different locations within a hospital's HVAC system. They identified genetic material from SARS-CoV-2, the virus that causes COVID-19, in one report, which can be found online as a preprint and has not gone through scientific examination. This suggests that HVAC systems may spread the virus.
Researchers could not determine whether the genetic material discovered could cause infection, and they noticed that no reported COVID-19 cases were linked to the samples found in the ventilation systems.
There is currently no other evidence that an air conditioning system can transmit COVID-19.
According to Edward Nardell, a Harvard Medical School professor of environmental health, immunology, and infectious diseases, the greater risk is that hot weather outside induces people to seek air-conditioned warmth indoors. Indoors, there is less ventilation and a greater risk of disease transmission.
"The air conditioner isn't doing anything in particular," Nardell claims. "It's the fact that you're indoors, not socially isolating yourself, just inhaling the air that others have just exhaled."
Shutting the doors and windows to trap the hot air outside effectively stops the fresh air flow, resulting in everyone in the room breathing and rebreathing the same air. If someone in the room is infected with COVID-19, they are exhaling the virus, which can persist in airborne droplets and infect others.
In contrast, if you were outside and near an infected person who breathed out any infectious particles, there would be a much more significant amount of air circulating to rapidly disperse and dilute those particles, eliminating the chance of the infection spreading to another person nearby. As a result, infectious disease experts believe that outdoor events and activities are less dangerous than those held indoors (though not wholly risk-free).
Another significant danger is that air conditioners, fans, or even an open window can produce powerful enough air currents to carry virus-infected droplets around a space. One study by the Chinese Center for Disease Control and Prevention found that this happened in January at a restaurant in Guangzhou, China. A person with COVID-19 infected five other people sitting at neighboring tables from 3 to 6 feet away. Scientists concluded that the small outbreak was triggered by intense air currents from the air conditioning unit above the diners, which were blowing virus-containing aerosols from an infected individual to others nearby, after analyzing video footage of the infected eateries and simulating virus transmission. The restaurant often lacked screens, preventing fresh air from entering and diluting virus particles in the air.
Aerosolized viral droplets travel in air currents, so even though you are socially distancing, you might not be safe if you are in a room with an infected individual where fresh air is not circulating. While no published studies have looked at how far COVID-19 particles can travel in the air, previous influenza research has shown that viral particles can travel up to 30 feet in the air.
This is only an issue in shared public spaces, to be precise. COVID-19 transmission through air currents or air conditioning systems is no more likely at home than transmission through direct contact or touching polluted surfaces.
It's not just the heat or the air conditioning that's a problem. Cold winter weather, which causes people to stay indoors and pump up the heat, creates an atmosphere with little ventilation, allowing viral particles to travel through the air and infect people.
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