Likelihood of false negative on COVID test can as high as 40 percent, county health officer says

After some Wayne County students tested negative for COVID-19 but were told by medical professionals to presume they were positive, local health officials are aiming to answer residents’ questions about how that happened.
A COVID-19 diagnosis can be made either through a laboratory or clinically, according to Wayne County Health Officer Dr. David Jetmore in an op-ed column sent to local media.
Jetmore said there are three laboratory tests in use for diagnosing COVID-19. They are the PCR test, the rapid test, and the antibody test.
The PCR test results take two to three days and have a positivity accuracy of close to 100 percent. That test measures the genetic material of the virus, he said.
The rapid test gives results in 15 minutes by measuring antigens of the virus. He said that test also has a high positivity accuracy of close to 100 percent.
The antibody test has no real place in diagnosing COVID-19 in that it only reveals that the person has had the disease at some time in the past, but Jetmore said it’s still unknown what that means in terms of future immunity.
In short, Jetmore said if either the PCR or rapid test are positive, a patient has COVID-19, but the dilemma comes from negative test results.
He said the PCR test can give false negatives, which means someone has the disease, but the test is negative.
The likelihood of a false negative on a PCR test can be as high as 40 percent if done too early in the infection, Jetmore said, noting the rapid test can yield 20 to 30 percent false negatives.
Jetmore said with a clinical diagnosis, the person is considered to have COVID-19 if he or she exhibits symptoms of the disease, which are fever, cough, shortness of breath, aching, sore throat, and loss of taste and smell.
“Many of these symptoms can be seen in other diseases, but loss of taste and smell coupled with respiratory symptoms particularly point to COVID-19,” Jetmore said.
Thus, medical professionals sometimes face a dilemma of a person with classic COVID symptoms and a negative test. In that instance, health officials recommend self-quarantining for 14 days.
Any child or adult, who is identified by the school as a close contact of a known positive COVID-19 individual, will be placed into a 14-day quarantine from the date of their last known exposure.
“Because of our concern for the health of everyone in contact with the affected person, we will always take the more cautious route,” Jetmore said. “Until a viable vaccine is available to us, contact tracing and isolation are the best tools we have to bring this epidemic under control.”