The University of Tennessee, Knoxville.

Getting it Right:

Testing Accuracy for COVID-19

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

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

March 31, 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 information on the accuracy of COVID-19 testing.  

False Negative and False Positive Rates of COVID-19 Test

Since there is currently no vaccine or drug(s) for preventing or treating COVID-19, it is essential to detect the disease accurately and at an early stage, and immediately isolate the infected persons from the rest of the population.
To determine whether a suspected person has COVID-19 or not, samples taken from the back of a person’s nose or throat are collected and submitted to a lab for detection of genetic material from the coronavirus.

Any diagnostic test for COVID-19 must correctly identify those with the disease as having the disease (sensitivity of the test) and those without the disease as not having the disease (specificity of the test).
In the US, the most commonly used test is the reverse transcription polymerase chain reaction (RT-PCR). This, and a variety of other tests using a slightly different PCR platform were approved by the United States Food and Drug Administration (FDA) and rapidly deployed under the Emergency Use Authorization (EUA). Currently, there are no published data on the performance of these tests in real-world situations.
Based on reports from studies done in China, the sensitivity of the COVID-19 test may vary based on site of swab collection. For instance, Yang and his colleagues evaluated the accuracy of the standard COVID-19 genetic test used in China (i.e. the RT-PCR) in different respiratory specimens. They reported a sensitivity of 54% to 73% for nasal swab specimens, and of 30% to 60% for throat swab specimens taken 0-14 days after illness onset. 
A different study by Wang and his colleagues reported sensitivities of 63% for nasal swab and 32% for throat swab specimens. Ai and his colleagues reported sensitivity of between 66% to 80% for throat swab specimens taken from patients with suspected COVID-19 .
These data imply that 27-46% of the people whose nasal specimens were assessed, and 20-70% of those whose throat swabs were assessed for COVID-19 were inaccurately told that they did not have the disease when they actually had it.
Given the highly contagious nature of COVID-19 (on average, each infected person can infect 3 other people, the low sensitivity for the test underscores the need for continued social distancing and other measures to combat the spread of the disease in the community and ensure that hospitals and centralized quarantine facilities do not get overwhelmed.
The low sensitives also show the need for caution in interpretation test results; if a person receives a negative RT-PCR test but suspicion for COVID-19 remains, the person should be isolated and re-sampled several days later.
A number of studies suggest that chest CT may complement clinical symptoms and genetic tests in early diagnosis of COVID-19. For instance, Ai and his colleagues demonstrated higher sensitivity (97-98%) for chest CT, a routine imaging tool for rapid diagnosis of pneumonia, than for RT-PCR test (66-80% sensitivity for throat swabs).
Moreover, they observed lung abnormalities typical of COVID-19 in chest CTs of patients with COVID-19 clinical symptoms but negative RT-PCR results. Xie and his colleagues reported negative RT-PCR tests for throat swabs despite chest CT findings suggestive of viral pneumonia in some patients who ultimately tested positive for the COVID-19 virus.

Among persons with a positive test result for COVID-19, there is a chance that some of them may not actually have the disease i.e. they may be false positives. There is no published data regarding the false positive rates for the myriad of tests being used across the US. 

How long, after exposure, does it take for the COVID-19 virus to be detectable?

At this time, no studies have been done to investigate how long, after infection, it takes for the virus to be detected. However, sampling early in the disease course may lead to a negative RT-PCR test compared to sampling later.
For instance, Ai and his colleagues reported that 23% of patients with suspected COVID-19 tested positive after an initial negative PCR test. Viral genetic materials have been reported to be higher soon after symptom onset (0-7 days) compared with later in the illness (See Yang et al. and Zou et al.).
A study performed in China by Yang and colleagues detected viral genetic material in the upper respiratory tract samples collected as early as 3 days after onset of illness.
Viral loads tend to be higher in the nose than in the throat (See Yang et al. and Zou et al.).

A list of testing site locations in Tennessee counties can be found here.

This brief is part of a series that will be produced by the CORE-19 team over the next few weeks forecasting the health and economic impact of the virus. The Department of Health for the State of Tennessee is also providing ongoing updates. As this is an emerging issue dealing with a novel virus, information included here is potentially subject to revision as new research and data emerge. 
More information can be found here:

Coronavirus-19 Outbreak Response Experts (CORE-19) 

Dr. Evah Odoi

Dr. Evah W. Odoi, PhD

Odoi is a Adjuct Professor in the Department of Public Health and in the Department of Biosystems Engineering and Soils Sciences at the University of Tennessee. She is interested in the connections between environmental and public health. Her current research interests include investigating environmental drivers of health disparities and forecasting disease risks.
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.
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. 

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. The information contained in this brief is for informational purposes only. No material in this brief is intended to be a substitute for professional medical advice, diagnosis or treatment, and the University of Tennessee makes no warranties, expressed or implied, regarding errors or omissions and assumes no legal liability or responsibility whatsoever for loss or damage resulting from the use of information provided.

Howard H. Baker Jr Center for Public Policy
1640 Cumberland Avenue
Knoxville, TN 37996
Phone: 865-974-0931
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