As coronavirus tests have become available in larger numbers, testing has shifted from individuals with symptoms to testing of individuals who may have been exposed to the novel coronavirus (COVID-19) but are asymptomatic. Testing of the entire workforce at some meat and poultry processing plants has been undertaken recently. In some instances, large numbers of workers are testing positive for COVID-19 without exhibiting symptoms of the illness.
I asked Anne Mardis O’Keefe, MD, MPH, senior epidemiologist, Douglas County Health Department, in Omaha, Nebraska, if the high number of workers testing positive for COVID-19 that are asymptomatic might tell us something about spread of the virus in the general population. She said, “The testing of these workers will not give us an estimate of the true infection rate because they are testing for presence of the virus by looking for the virus’ RNA.”
She explained that the workers at a plant are not a representative sample of the population at large just as testing for health care workers and other first responders would not be. “True illness rates are estimated by doing antibody testing in a statistical sample of the general population,” she said.
As far as the number of asymptomatic positive tests go, Mardis O’Keefe said: “Regarding the RNA testing (aka PCR testing), people may be positive 48 hours before symptoms or may be asymptomatic. They also may have detectable RNA for weeks after illness.” She said that she is hearing that many people who do not have symptoms when they test positive end up developing symptoms soon after. Which means they were really "pre-symptomatic," not asymptomatic.
Only time and antibody testing will be able to give us a clearer picture of how many people have been exposed to COVID-19 and have not gotten sick or who have gotten ill and have recovered. For now, efforts will continue to focus on limiting everyone’s exposure to the virus. I will be hoping that testing will show that the virus causes less illness and death in otherwise healthy individuals than originally thought.
View our continuing coverage of the coronavirus/COVID-19 pandemic.
