Robin Scholz/The News-Gazette Champaign-Urbana Public Health District Administrator Julie Pryde talks about flattening the curve of the virus as Dr. Robert Healy of Carle listens at a press conference at the Champaign-Urbana Public Health District office in Champaign on Sunday, March 15, 2020.

Listen to this article

Q: How much is known about the accuracy of COVID-19 tests? How likely is it that there are false negatives or false positives, and what would cause that? And can you explain why it takes so long to get test results back?

A: The accuracy of the tests is very high. The test specifically looks for a very unique part of the COVID-19 coronavirus genome that is not shared with other organisms, and tests have been validated to ensure they do not give a signal in the absence of COVID-19 coronavirus.

So chances of a false positive are extremely low when the test is run correctly.

Chances of a false negative are possible if you are not shedding very much virus at the time you are tested, but for patients who are symptomatic, false negative rates are probably going to be low. Exact numbers on this are hard to come by.

The reason testing results are taking so long is that there is a national shortage of the necessary supplies to run the tests. This includes everything from the swabs needed to collect material from patients to test to the specific materials needed to run the test itself. That means there is much more demand for tests than there is currently capacity to run them. This is leading to major backups.

If all supplies were available, the test itself only takes two to three hours to run.

(Pryde answered this question with an assist from Christopher Brooke, virologist and professor of microbiology at the University of Illinois.)