The University of Tennessee, Knoxville.

COVID-19 Case Reporting in Tennessee Explained

A Policy Brief by the Howard H. Baker Jr. Center for Public Policy

in Partnership with the Coronavirus-19 Outbreak Response Experts (CORE-19)

April 3, 2020
Tennessee State Capitol and Flag
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?
This is a tough question and should be interpreted on a case-by-case basis. While your roommates might be free from COVID-19, it is possible that the test produced a false negative result. The sensitivity (proportion of truly diseased individuals who tested positive) of COVID-19 tests is not 100%. As of April 1, 2020, there is no peer-reviewed publication on the diagnostic test performance of COVID-19 tests in the United States.  
Assuming a test with sensitivity of 85% is applied to 100 truly infected COVID-19 patients, only 85 patients will get a positive test result; the other 15 would have a negative result (false negatives). You can read more about false positives and false negatives for COVID-19 in a brief we recently posted on the topic. 
Alternatively, your roommates may not have COVID-19 (true negatives) but there are certainly other infectious organisms going around too. Out of an abundance of caution, it is best to practice the recommended social distancing even after a colleague/loved one tests negative for COVID-19. Please stay safe and well.
More information can be found here: http://core19.utk.edu/
Send your additional testing/results related questions to Dr. Chika Okafor or contact the CORE-19 research team. 
okaforch@utk.edu  | core19@utk.edu | 865-321-1299
Disclaimer: the information in this policy brief was produced by researchers, not medical or public health professionals, and is based on their best assessment of the existing knowledge and data available on the topic. It does not constitute medical advice and is subject to change as additional information becomes available. 

Coronavirus-19 Outbreak Response Experts (CORE-19) 

Dr. Chika Okafor, DVM, MS, PhD

Okafor is an assistant professor in the UT College of Veterinary Medicine, Department of Biomedical and Diagnostic Sciences. His areas of expertise are Veterinary Public Health, Food Safety and Epidemiology
Dr. Marcy Souza

Dr. Marcy J. Souza, DVM, MPH

Souza is an associate professor and Director of Veterinary Public Health in the UT College of Veterinary Medicine.  Her teaching and research focuses on zoonotic diseases and food safety issues. 
Dr. Kathleen Brown

Dr. Kathleen C. Brown, PhD, MPH

Brown is an Associate Professor of Practice in the Department of Public Health and the Program Director for the Master's in Public Health (MPH) degree. Her research focuses on the health and well-being of individuals and communities. She has experience in local public health in epidemiology, risk reduction and health promotion.
Dr. Katie Cahill

Dr. Katie A. Cahill, PhD

Cahill is the Associate Director of the Howard H. Baker Jr. Center for Public Policy. She also is the Director of the Center's Leadership & Governance program and holds a courtesy faculty position in the Department of Political Science. Her area of expertise is public health policy. She leads the Healthy Appalachia project. 
Dr. Kristina Kintziger

Dr. Kristina W. Kintziger, PhD, MPH

Kintziger is an Assistant Professor in the Department of Public Health and the co-Director of the Doctoral Program. She has worked in academia and public health practice, and comes to Tennessee from the Florida Department of Health, where she worked as an epidemiologist and biostatistician. She is an environmental and infectious disease epidemiologist.
Dr. Matthew Murray

Dr. Matthew N. Murray, PhD

Murray is the Director of the Howard H. Baker Jr. Center for Public Policy. He also is the Associate Director of the Boyd Center for Business and Economic Research and is a professor in the Department of Economics in the Haslam College of Business. He has led the team producing Tennessee's annual economic report to the governor since 1995. 
Dr. Agricola Odoi

Dr. Agricola Odoi, BVM, MSc, PhD

Odoi is a professor of epidemiology at the University of Tennessee College of Veterinary Medicine. He teaches quantitative and geographical epidemiology and his research interests are in population health and impact of place on health and access to health services. He was a public health epidemiologist before joining academia.
Howard H. Baker Jr Center for Public Policy
1640 Cumberland Avenue
Knoxville, TN 37996
Phone: 865-974-0931
Email: bakercenter@utk.edu
Online: bakercenter.utk.edu
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