It’s a little stressful being around other people when one of the masked strangers you pass is unwittingly carrying SARS CoV-2, the virus that causes COVID-19. And if you live in a condominium complex or apartment building, people can be difficult to avoid. But once you’ve got through the many common areas – dodging neighbors in the lobby, avoiding railings on the stairs, pressing elevator buttons with your elbow – and entering your own room, you can wash your hands, remove your mask, and stop worrying do, right? It’s not like the virus blows through the air vents while you sleep, like it does in a scary movie, is it?
The vast majority of evidence suggests that SARS CoV-2 is mainly transmitted through the large respiratory droplets that infected people expel when they sneeze or cough, said Dr. Cassandra Pierre, assistant professor of medicine at Boston University School of Medicine and a doctor at Boston Medical Center. Both US Centers for Disease Control and the World Health Organization claims that infections occur primarily through personal contact at close range or from touching a contaminated surface such as a doorknob or counter, on which virus-laden droplets land and can survive for up to 72 hours. “To date, we have not seen any evidence of air circulation in buildings,” said Pierre.
“But there is also evidence that there could be a hybrid form of transmission – not just droplets, but possibly air or aerosol transmission as well,” she said. Aerosols are smaller, microscopic particles that stay in the air and can travel long distances.
For example, researchers from the University of Nebraska tested the hospital rooms of COVID-19 patients and found virus particles remaining in the air 6 feet or more from the patients – even a few hours later. Other preliminary studies have found similar results. “But there are always reservations about such studies,” warned Pierre. “They found evidence of viral particles and viral RNA, but that doesn’t mean it’s a viable virus,” she said. In other words, it is not known whether these particles could infect anyone else.
And so far Pierre said: most of this evidence was accompanied by an “aerosol generating procedure”, for example by a patient who is being intubated. “This creates these high-speed aerosols and they are expelled into the air,” said Pierre, which may not be the case in everyday life. “Nobody should be intubated in the lobby of their building, one would hope.”
However, some experts say there is a strong possibility of airborne transmission, even during routine conversations. Scientists at the National Academies of Science, Engineering and Medicine in April submitted a letter to the White House that claims so much.
Joseph Allen, Assistant Professor at the Harvard School of Public Health and Director of the Harvard School of Public Health Healthy Buildings Programwarned since the beginning of February This transmission takes place in the air. “And since then, every piece of new evidence has supported this,” Allen said.
In one upcoming paper (not yet peer-reviewed)Allen and Virginia Tech Environmental Engineering Professor, Linsey Marr, state that there are documented cases of transmission by asymptomatic individuals who, by definition, would not cough, sneeze, or spray large droplets.
“There are studies now showing that we can detect viral RNA in places where it could only get there by airborne transmission,” Allen said. He also cites evidence from various outbreaks, from a cruise ship to the Biogen conference to a choir practice that infected a number of singers despite a series of precautionary measures. “You’ve been taking this body of evidence since January, it’s clear to people in my field that there is an airborne transmission,” Allen said.
If SARS CoV-2 can be carried by smaller airborne particles, it will present new challenges – as well as solutions – to contain the spread, especially in large buildings. “Because of this, control strategies that affect the ventilation system are critical,” said Allen.
Fortunately, there’s a pretty simple solution that Allen said would make sense even if we weren’t in the middle of a pandemic. “We can use highly efficient filters for the circulating air, which can be very effective at catching particles in the air,” he said.
If you live in a mechanically ventilated building, Allen suggested asking the landlord or manager about the HVAC system: does it bring in fresh outside air? How is air handled when it is circulated throughout the building? “Make sure they have highly efficient filters, a MERV 13 or higher,” he added, referring to the air filter rating system.
Contrary to some misunderstandingsAccording to Allen, HEPA filters should be very effective at trapping SARS-CoV-2 particles. “Filters are rated based on the particle size against which they perform worst,” said Allen. The 99.97 percent efficiency you see with a HEPA filter applies to 0.3 micron particles. “But it works even better on smaller or larger sizes,” he said.
The American Society of Heating, Refrigerating and Air Conditioning Engineers offers similar guidance. “Airborne transmission of SARS-CoV-2 is so likely that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilation and air conditioning systems, can reduce exposure to air, ”the trading group said in a Explanation In April.
A lower-The technical solution is simply to let more fresh air into the building. Like washing your hands or covering your cough, Allen said, ventilating rooms with outside air is a basic public health practice and can dilute contaminated indoor air. “If you have operable windows, keep your windows open,” said Allen. For residents who are concerned about the air circulation in their building, he added, “An additional control strategy can be the use of portable air purifiers. If they have a HEPA filter and are the right size for the room, they can effectively capture particles in the air. ”
An even less likely, but definitely more repulsive, transmission path could be the plumbing network of a building. “As little as we know about air, we know a lot less about plumbing,” said Pierre. “We know the virus can be shed in the stool,” she said, and could live in sewage if it’s like other coronaviruses. Pierre points to a famous case in Hong Kong during the SARS outbreak in the early 2000s, when the virus spread to more than 300 people in the Amoy Gardens residential complex – largely through open drains in bathroom floors that allowed aerosols from infected waste to enter migrate throughout the home.
This is obviously a frightening and disgusting prospect, Pierre admitted, but there are seldom such drainage systems in the United States. (If you’ve ever wondered why most drains have a U-shaped bend, you want water to stay in the pipe and keep sewage gases from rising again.) Still, it’s worth making sure your drains are working properly.
Allen adds that in addition to washing hands after using the bathroom, closing the toilet lid before flushing and running the exhaust fan is good practice. “Several reports have now shown that this virus was found in stool in children and adults several weeks after infection, and we know that flushing the toilet produces bioaerosols that can remain in the air,” Allen said. (And don’t worry: bathroom exhaust fans generally vent directly outside, not back into the building.)
The residents of a large building just have to stay cautious and vigilant, Allen said. In addition to general precautions such as frequent hand washing and social distancing, both Pierre and Allen recommend wearing a mask outside of your home, including in the elevator and in all public areas of your building, to protect yourself from inhaling infected particles – regardless of their size.
“These are the areas where you are more likely to breathe the air of someone who is sick,” Allen said.
Jon Gorey blogs about houses on HouseandHammer.com. Submit comments to [email protected]. Follow him on Twitter at @jongorey. Subscribe to our free real estate newsletter at pages.email.bostonglobe.com/AddressSignUp.