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COVID-19 Rate of positivity: What You Should know

 

People have been learning a lot of new skills in the world of COVID-19: bread baking, sewing, TikTok dances, and epidemiology terms. The newest term being rate of positivity. So, what exactly is rate of positivity? What can it tell us? And, how can we use it?

 

Rate of positivity =

 

 

 

If you multiply that by 100, you get the percentage of tests that are positive. Pretty simple.

Now we get into the complicated part. What does rate of positivity tell us and how can we use it during this COVID-19 pandemic?

The WHO recognizes that a rate of positivity of 5% or less indicates that a country, state, or region is conducting sufficient testing during an outbreak. Why? Because it tells us that enough people are being tested and that healthy people are being included in the data. If we know that healthy people are being included, then so too are asymptomatic or presymptomatic carriers and we will have a fairly complete picture of transmission of the disease such as COVID-19.

On the contrary, if positivity rate is greater than 5%, that indicates that only the very sick or symptomatic are being tested and that asymptomatic and presymptomatic carriers are not. This is especially concerning if transmission can occur through asymptomatic carriers, such as is suspected of COVID-19. In this scenario, asymptomatic or presymptomatic people are missed, making a true picture of disease transmission impossible.

Since COVID-19 testing is becoming more widespread in the United States, officials are now able to use the rate of positivity in the decision-making process, and it should be, with some caution.

Rate of positivity viewed alone can be a tricky metric because there are numerous factors that go into its calculation. Let us look at a few scenarios that could occur when a state increases the number of tests performed:

  1. Increased testing →The rate of new cases remains stable: this will result in a decrease in then rate of positivity.
  2. Increased testing → The rate of new cases also increases, then the rate of positivity might not change.
  3. Or, if there are more new cases than there are new tests, the rate of positivity could even increase.

Rate of positivity is an invaluable tool in disease tracking because it indicates that we are conducting enough testing to capture the entire picture of transmission. Rate of positivity can be used to help decision makers decide whether or not enough resources are being allocated to testing. If the rate is above 5%, more resources should be allocated to testing. If it is below 5% than it is likely that no additional helpful information would be gained from additional testing, and that any additional resources allocated to testing would not provide any more useful information.

Rate of positivity, alone, does not indicate anything about rate of transmission or more importantly healthcare capacity. Public health professionals and decisions makers need to continue to look at the whole picture during this COVID-19 pandemic. This includes but is not limited to, the number of tests performed, number of positive cases, number of hospitalizations, ICU utilization and recovery rates, when evaluating opening procedures. And even more importantly, decision makers need to evaluate trends in the changes in these numbers, especially the number of hospitalizations and ICU utilization which are not influenced by the interaction between testing rate and true number of cases. If the number of hospitalizations is rising it is because there is a problem and is not an artifact of increased testing. ICU utilization needs to be closely monitored because until there is a vaccine or a cure, the availability of treatment is the most important defense against people dying from COVID-19. The main goal of social distancing and non-pharmaceutical interventions is to prevent the healthcare settings from being overwhelmed with COVID-19 patients.

It is also extremely important to be mindful of the lag, or time between a change and the reaction. The most important in the case of COVID-19 is the incubation period, which is up to 14 days. If an area reopens and does not see increased cases for a week, that does not necessarily indicate that they are in the clear. The expected spike, if there is one is going to be around 2-weeks later, and this is the period that needs to be monitored and evaluated most closely.

The COVID-19 pandemic continues to be fluid and evolving, and the deluge of information (and misinformation) is constant and may seem overwhelming. We are here to help you streamline and interpret this information, and to guide you and your business about the best strategies for characterizing risk and reducing exposure in your workplace. Reach out to our experts at solutions@cogencyteam.com.

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