As the summer heat and new cases of the novel coronavirus continue to surge in much of the country, scientists are warily watching what potential impact retreating into air conditioned spaces may be having on the further spread of the virus.
Under normal circumstances, health care professionals encourage the public to seek refuge from high temperatures in the comfort of an air-conditioned space. But these are hardly normal circumstances.
While individuals can take steps to protect themselves, a growing body of research suggests that indoor spaces with poor ventilation or lack of new air can raise the risk of the virus' spread, according to infectious disease aerobiologist Dr. Donald Milton of the University of Maryland.
“Anytime we are going into a closed environment, we are at higher risk,” Milton told ABC News. He added that he was most concerned about people “going to a cooling center where ... the air conditioning is not filtering air or bringing in outside air -- and a lot of people are close together.”
Milton's worries were in part formed by research he and an international team of scientists published earlier this month that looked at the spread of the influenza virus, which causes the seasonal flu. The research found that the flu virus might be spread through the air, as fine droplets, rather than through large droplet spray, as was previously believed.
Moreover, the research revealed the virus’s infection rate appeared to drop in well-ventilated areas. Since both influenza and COVID-19 are respiratory viruses, Milton said his findings could mean that the types of closed spaces people typically go to escape the summer heat, when crowded with people close together, could also be ideal locations for virus spread.
And though Milton said he was especially concerned about cooling centers, a study recently published by researchers at the University of Minnesota and undergoing peer review suggested that the particular indoor setting and even the position of the ventilation could impact how well it did against potential viral-containing particles. With schools scrambling to prepare for fall, the University of Minnesota study included a classroom simulation.
Dr. Edward Nardell, a professor at Harvard Medical School, previously said that lower-risk spaces, such as office buildings, still often also force people to rebreathe non-fresh air.
In a recent presentation, Nardell cited his work with drug-resistant strains of tuberculosis as a possible parallel to the current coronavirus situation, noting to The Harvard Gazette in late June that, “As people go indoors in hot weather and the rebreathed air fraction goes up, the risk of infection is quite dramatic.” Nardell added that the same principle applies to extremely cold weather, which also forces people indoors.
Some infectious disease experts also suggest that recycled airflow caused by air conditioners could alter the widely held understanding – shared by both the World Health Organization and the Centers for Disease Control and Prevention – that virus-carrying air droplets rarely travel further than six feet. It was a fear raised months ago in a CDC-published, peer-reviewed study drafted by Chinese government researchers.
The Chinese study focused in on the circumstances surrounding a small outbreak that was traced back to a restaurant in Guangzhou, China – a coastal city of 13 million situated just north of Hong Kong. At the restaurant, according to the studies, 10 diners seated at three different tables inside the restaurant’s windowless, third-floor dining space became infected with the virus within two weeks of having lunch there.
Some of the infected diners sat more than 14 feet, or more than double the accepted distance of droplet distance, away from the “index patient” – the person believed to have brought the virus into the restaurant.
The expanse between diners led researchers to conclude that “strong airflow from the air conditioner could have propagated droplets” between the restaurant's tables, effectively suggesting that air conditioning units spread infectious droplets with impunity.
Milton told ABC News that the initial Chinese study “does point to the virus being able to survive in air for a while and travel a little bit farther.”
For individuals looking to take refuge indoors, Nardell said they can better protect themselves by using face coverings and exercising social distancing.
But Nardell and others said people who own or run the facilities can take steps as well.
To combat the spread of the virus in settings like offices, Nardell suggested administrators invest in germicidal lamps, which use ultraviolet light to kill floating pathogens as they circulate through the air.
Others suggested the current situation can be used as an opportunity to upgrade air conditioning filtration systems.
Dr. Erin Bromage, a biology professor who researches infectious diseases at the University of Massachusetts-Dartmouth, says that “hotter weather will make fewer commercial buildings acceptable.”
Since most of these buildings recirculate air, Bromage said building operators should install air filters. These air filters are measured in strength by what is known as a Minimum Efficiency Reporting Value -- or MERV -- rating, which indicate how small of a particle they are capable of trapping.
New York State, for example, recently issued guidelines requiring large shopping malls to install MERV-13 rated filters before they re-open, which is the filter strength Bromage has endorsed.
And what about taxis and ride-sharing vehicles, where passengers likely do not have the ability to swap out air filters?
“Sharing a car is one of the highest-risk interactions I have had to look at in my life,” warned Bromage.
To reduce the risk, Bromage said passengers should ask their driver to turn on the air conditioning, turn off the air recycler, and, perhaps most importantly, lower the windows.
“In cars and ride sharing, we want the windows open,” said Bromage. “It makes things safer.”
What also appears to make things safer are the basic steps experts have long advocated. James Malley, Jr. is a professor of civil and environmental engineering at the University of New Hampshire. He has spent decades studying ways to root out pathogens in air and water.
Malley Jr. told ABC News the best ways to protect yourself and others against the virus are also the easiest.
“A lot of common sense things like increasing fresh air, not having a lot of people in an enclosed space, wearing masks,” he said. “That all makes a difference.”
What to know about coronavirus:
- How it started and how to protect yourself: Coronavirus explained
- What to do if you have symptoms: Coronavirus symptoms
- Tracking the spread in the U.S. and worldwide: Coronavirus map
Jay Bhatt, a practicing internist and Aspen Health Innovators Fellow, is an ABC News contributor.