The theory uses a mathematical calculation to determine the risk of virus spread in different situations.

A professor at Johns Hopkins University is using a little-known equation to help determine the chances of a person contracting the coronavirus. Professor Rajat Mittal of the Johns Hopkins Whiting School of Engineering has co-authored a new paper that uses the Contagion Transmission Inequality theory to determine the risk an individual has to catch the coronavirus based on circumstances and surroundings. It is based on the Drake theory, an equation that was used to estimate the likelihood of finding alien life in the Milky Way. 

Contagion Transmission Inequality, or CAT Inequality for short, gives numerical assignments to factors like number of virus droplets, droplets that penetrate a mask, and duration of exposure. Seven months into the coronavirus pandemic, scientists have conceded the virus is spread from person to person via respiratory droplets. But how much and for how long, still isn’t clear.

CAT Inequality Theory

Courtesy Johns Hopkins School of Engineering

The model has nine variables in three categories, including the infected host, environmental variables, and susceptibility. The result can be different based on different factors—for instance, using an example of two people working out at the gym.

"Imagine two people on treadmills at the gym; both are breathing harder than normal. The infected person is expelling more droplets, and the non-infected person is inhaling more droplets. In that confined space, the risk of transmission increases by a factor of 200,” says Professor Mittal. 

Pretend both of these people are wearing N95 masks, and the risk factor drops to a one percent chance that the healthy person will get the virus. The authors of the paper hope CAT Inequality can be used by public health professionals, scientists, policymakers, and even individuals to evaluate everyday situations and determine risk. 

The study was co-authored by Charles Meneveau, a professor of mechanical engineering, and Wen Wu, an assistant professor of mechanical engineering at the University of Mississippi.