R-naught (R0) and How to Understand it: A Basic Guide

R0 (pronounced R naught) is a term news reports have been using the start of the COVID-19 pandemic. It is a term used in epidemiological and statistical circles to try and break down how contagious a pathogen is. In layman’s terms, it is a marker to see the rate of illness is going up or down in population, and that indicates what scientists believe the infection rate in the future will be.

The R in R0 stands for reproduction, and the 0 or naught in statistics typically stands for the default assumption. The other side of the equation is a number, which for most disease is below or at 1, but in the case of an epidemic or a pandemic, this number will rise above one. Whatever the number is, it is assumed that the number represents how many people will get sick, on average, for every one person currently infected with the pathogen.

A couple of things should stand out at this point.

First, R0 can only be applied to diseases that spread when a person is infected. R0 inherently assumes this is a rate of infection, based on a person being infected. It is not a number that can be used on a non-spreadable event, such as cancer or an allergic reaction to a local pollen. 

Second, lower numbers are better. More on this in a little.

Third, that R0 is an assumption, or prediction for the future. By now, most people are aware that there are several COVID-19 variants, and there is often the discussion of spreadability of each of these variants. These conversations are based on the projected R0 of the variant. 

Because R0 is an assumption and it applies only to diseases that spread through human interaction, human behavior affects R0, and thus affects what scientists believe the incident rate of the disease will be in the future.

In short, there are three possible solutions. An R0 around 1 means that it is expected that in the future, the same number of people will be sick as they are today. As R0 trends towards 0, the disease is becoming extinct, and as it rises above one, scientists will expect the potential for an epidemic or pandemic. For example, when this article was published the variant of COVID-19 Omicron was the dominant variant, and it is currently estimated at R0 = 7. This means that for every person that gets Omicron, we can expect 7 more people to get it from them. In 2014, the Ebola outbreak had an estimated R0 = 1.51.

As mentioned previously, human behavior can affect the R0 of a disease. Let’s assume that 4 people are sick with a flu. 3 of them choose to stay home in bed, and one goes a dinner party with their partner and another couple that night. All 3 of the other people get sick. If scientists studied this situation, they would expect R0 to equal .75 (meaning the disease was winding down). Similarly, if all 4 people chose to go out with just their partners and they got sick, scientists would expect R0 to equal 4 in 1 (meaning that the disease was staying its course).

Now let’s suppose all 4 people chose to stay home and got no one else sick, in this case scientists would anticipate R0  to equal 0, meaning no new cases would arise.

At illumiPure, our goal is to create indoor environments with an R0 = 0. That is why we focus on disinfecting surfaces, restoring your air to its cleanest form, and monitoring your surroundings to alert you if something is wrong. This is our formula to create an R0 = 0. But we can’t do it without you. So make sure you cover cough, wear a mask if appropriate, and wash your hands. Together, we can stamp out infectious diseases and reduce their spreadability to nothing.

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Chris Romani

Chris Romani is the Chief Marketing Officer of illumiPure. After receiving his Master's Degree, Chris has worked for the last decade on the marketing of manufactured products. Chris has advocated for transparency of health-related data of these products and sees health and wellness as a primary purchasing influencer of many products today.

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