Using publicly available data from emerging research on COVID-19, this brief was written and reviewed by the Coronavirus-19 Outbreak Response Experts (CORE-19) at the University of Tennessee, Knoxville. It provides answers to some of the most frequently asked questions regarding case reporting and testing in the State of Tennessee.
Understanding Reported Results
As we move forward through the COVID-19 pandemic, the reported results can sometimes be overwhelming. It can be difficult to sort through the COVID-19 coverage that continues to impact our everyday lives. Here are some frequently asked questions, designed to provide some clarity to this reporting.
What is the best explanation for the daily increases in positive case counts of COVID-19 in TN?
The number of positive cases (patients with positive diagnosis of COVID-19) in TN is increasing daily partially because the number of suspected individuals tested is also increasing daily. The average daily increase in testing between March 28 and April 1, 2020 is 10 to 16%.
As more testing is performed, more positive cases will be identified. Physicians are still limiting who can get a test, and individuals need to meet certain symptomatic parameters before being tested.
Currently, with our limited/targeted testing, the number of cases reported generally are clinical cases. But as testing becomes more available, the number of cases will likely increase as asymptomatic people are screened and identified as positive for COVID-19.
It is important to state that the population currently being tested is not representative of the general population (only includes individuals with clinical presentations of COVID-19 or those traced to have been exposed to known cases) and as such you expect the case count to be higher in this specific population.
Test results would make more sense if you know the total tests performed from which the cases were identified. As an example, 1,800 cases out of 2,000 tests performed (90% positive) is more concerning and different from 1,800 cases out of 20,000 tests performed (9% positive).
Although the reported case count is valuable, it is not as informative as the proportion of test positives to the total tested individuals (clinical prevalence of COVID-19). This proportion of test positives is more accurately an estimate of disease burden in the tested population of currently symptomatic people.
What is clinical prevalence of COVID-19?
Clinical prevalence is the proportion of the clinical population (individuals with clinical symptoms of COVID-19 or those traced to have been exposed to known positive cases) who tested positive for COVID-19. This expression is obtained by dividing the total case count by the total number of individuals tested.
For Tennessee, the clinical prevalence on March 24, 2020 was 6% (of every 100 tested individuals, 6 had a positive COVID-19 diagnosis), but the daily cumulative clinical prevalence has risen to 8.3 % on April 1, 2020.
As of April 1, 2020, a cumulative total of 32,452 tests had been completed in Tennessee and 2,683 cases have tested positive (8.3%) since the index case of COVID-19 was identified in Tennessee on March 5, 2020.
You may find this expression reported as % positive in some media outlets. Remember, this clinical prevalence is different from population prevalence of COVID-19.
How is clinical prevalence different from population prevalence with respect to COVID-19?
Because the current testing of COVID-19 is mainly restricted to individuals showing clinical symptoms or contact tracing of potentially exposed individuals, clinical prevalence is the measure of the burden of COVID-19 among the tested individuals.
This population is a biased sample and the burden of disease is higher than the general population. The population prevalence (proportion of the general population that tested positive) of COVID-19 can be obtained when a random sample of the population is tested for COVID-19. This approach would produce the true estimate of the burden of disease in the general TN population.
My roommates returned from a COVID-19 hotspot, showed mild symptoms of flu but their COVID-19 tests were negative, should I still be concerned?