As the festive season approached, two professors developed a tool to assess the risk of COVID-19 infection in various indoor environments and made it available to the general public.
This interactive website, entitled COVID-19 Indoor Safety Guideline, developed by Professors Martin Bazant and John Bush of the Massachusetts Institute of Technology, provides calculations that can be used to estimate how many people can be in an enclosed space and how long before they are theoretically exposed to the virus.
Both Massachusetts Institute of Technology professors Martin Bazant and John Bush, with backgrounds in fluid mechanics and mathematics, are working to advance guidance on containment of the virus through a data-driven risk assessment approach.
Working with Kasim Khan, an energy consultant and recent graduate student, Bazant and Bush developed the digital simulation and incorporated several factors such as room size, ventilation, use of masks and the number of people present to help users determine risk levels.
Users can specify values for each of these variables and the module generates risk assessments accordingly. It gives users an estimated time in hours or days during which groups of people of different sizes could theoretically interact before they become infected with the virus, assuming that a person is already infected.
“The security guideline is simple enough to show trends and allow for useful calculations without neglecting quantitative relevance,” Bazant told Washington Newsday, noting that it helps to “illuminate the relative importance of using face masks, good ventilation, low population density, soft speech, light activity, air filtration and moderately high humidity, roughly in that order, as strategies to contain transmission.
The application is attracting public attention as corona virus transmission is rampant in the USA. In December, the country diagnoses cases, admits hospital patients and records a frightening number of deaths. The onset of colder temperatures poses a new threat to the further spread of COVID-19. People gather indoors, where the risk of contracting the virus is higher, especially at a time of year when experts believe there is an increased risk of transmission by itself.
Health authorities are offering a range of containment tactics aimed at reducing the spread of COVID-19, with face masks and a physical distance of two meters being some of the most effective measures. And a health expert told Washington Newsday that while the digital tool can serve as a guide for individuals during the pandemic, users should not consider the results achieved as absolute.
The risk assessment app does not take into account situations where none of the people present wear a face mask. In an FAQ section that appears next to the simulation itself, the creators point out “an additional risk of short-range transmission” of COVID-19 if neither masks nor face shields are worn. They estimate this additional risk in a scientific paper, which is also published, but is currently being reviewed by colleagues.
Bazant and Bush defined the parameters of the module after analyzing a handful of super-spreader events that had occurred worldwide during the earlier part of the pandemic. It is essentially rooted in the idea that COVID-19 spreads primarily by air – a conclusion Bazant expressed to Washington Newsday became apparent during the research process.
The consistency of their findings, Bazant said, “provides strong support for the already overwhelming evidence of airborne transmission as the dominant mechanism for the spread [of COVID-19],” he said.
“John [Bush]’s work on the fluid mechanics of coughing and sneezing made it clear that pathogens carried by exhaled aerosol droplets can spread much further than a meter,” Bazant said. The professor added that his experience in chemical engineering suggested that “airflow properties, room occupancy and exposure time may be more important variables controlling transmission than physical distance.
Information on the primary modes of transmission of COVID-19, which are the most common, has developed over the course of the pandemic. The Centers for Disease Control and Prevention (CDC) originally believed that transmission occurs through close contact with an infected person, when respiratory particles carrying the virus are most likely to be transmitted to others by coughing, sneezing, or general breathing. Direct contact with an infected person through a hug or handshake and sometimes through contact with a contaminated surface was also quickly recognized as a form of transmission.
This early understanding of how the virus can spread formed the basis for the CDC’s initial guidelines for harm reduction. They were issued shortly after the outbreak began in the United States and suggested that everyone in public places should wear face masks, maintain a distance of six feet from people outside their immediate household and wash their hands frequently to reduce the risk of transmission.
Although the CDC continues to believe that COVID-19 is most likely to spread in close contact scenarios, it issued additional guidance in the fall recognizing the potential for airborne transmission of COVID-19.
“It is possible that COVID-19 can spread through droplets and airborne particles created when a person who has COVID-19 coughs, sneezes, sings, talks or breathes,” according to a note posted in December on one of the CDC’s virus resource pages. “There is growing evidence that droplets and airborne particles are suspended in the air and can be inhaled by others and can travel distances greater than 1.5 meters (e.g., during choir practice, in restaurants, or in fitness classes)”.
The ongoing debate about the airborne spread of COVID-19 transmission has continued throughout the year. While some scientists, such as Bazant and Bush, believe that this is a dominant source of the virus’ spread, others say that outbreak patterns indicate that this mode is relatively rare. The CDC bases its recommendations on the latter view. It notes that epidemiologists would expect a primarily airborne virus to infect a population faster and more aggressively than COVID-19 has been infecting the United States since March.
Dr. Amesh Adalja, a senior scientist at the Johns Hopkins Center for Health Security whose work focuses on infectious diseases, pandemic preparedness and biosecurity, considered the basic hypotheses of the COVID-19 guideline on indoor transmission security as her most important limitation. However, he pointed out the current lack of “risk assessment” tools available to the general public.
“I believe that in general it makes sense to do such things,” Adalja told Washington Newsday about the risk assessment application, saying that models like this one can be an important resource for people to more concretely assess transmission risks. “It is definitely necessary for people to have an idea of the relative safety of certain activities, and then they can make much more informed decisions”.
“I would simply say that this is about airborne transmission, and it could be something that is not necessarily applicable to everyday situations because it is very much focused on air,” he continued. “And I think that’s just something to keep in mind when you look at it.”
Washington Newsday turned to the CDC for comment but did not receive a response in time for publication.