Lost in the call for tests to identify the coronavirus, is the need for a test showing if someone has unknowingly already had it. After all, the illness can closely resemble the flu and present as a mild illness in most cases.

While a diagnostic test for the illness can spot the genetic fingerprint of COVID-19 in a person's saliva, it can only detect it during the brief period it is active. These are called PCR tests, and while they can be useful in quickly identifying and isolating those who are contagious, they cannot tell whether a person once had coronavirus and fought it off.

A so-called serology test looks into a blood sample for disease-specific blood proteins known as antibodies, then determines if your body's immune system is pre-loaded to fend that illness off the next time you are exposed. Because it takes the body time to develop antibodies, an antibody test is less effective at identifying new cases, but decidedly important for telling society that's fighting a sometimes invisible illness whether it is safe to return to normalcy.

This makes the news all the more meaningful that Mayo Clinic has announced it is just weeks away from delivering an antibody test for coronavirus. Only Singapore has  developed such a test, and it has yet to be validated.

"We are actively pursuing options for serologic testing for COVID-19, which would allow us to determine whether a patient has developed an antibody response to the infection," said Matthew Binnicker, Ph.D., and Elitza Theel, Ph.D. of the department of laboratory medicine at Mayo Clinic in a statement.

The researchers are collaborating with outside diagnostic companies who have developed assays to find the antibodies. They hope to soon be able to determine "how many people in the population have been exposed to this virus."

"We hope to have the first test available within the next two to three weeks."

They added that the antibody test can serve as a supplemental diagnostic method to use alongside PCR. They also hope that by identifying immune individuals who could then donate plasma with coronavirus antibodies for persons at risk, the test could hold the promise of providing quick-acting so-called "passive immunity" to ill patients and potentially to at-risk healthcare workers.

"If you got a random sample of the population and gave them an antibody test, that's definitely really useful information," said Kris Ehresmann, director of infectious disease for the Minnesota Department of Health. "With all that said, it's clearly not for answering the question of, in real time, does someone have the illness now."

But another goal is reaching a point, without overwhelming the health care system, at which enough persons have been exposed to the virus for society to have developed so-called herd immunity. With that in mind, knowing whether large numbers of people have already had the virus suddenly becomes a critical piece of information.

"We're still learning about the virus," Ehresmann says. "But a lot of leaders in this field now believe that infection with coronavirus will provide immunity. If that's the case, that information about how much of the public has been infected becomes incredibly valuable."

Health officials have opened a school and child care hotline at (651) 297-1304 or (800) 657-3504.

The Minnesota Department of Health coronavirus hotline can be reached at (651) 201-3920, or (800) 657-3903 toll free. It is now open from 7 a.m. to 7 p.m. daily.

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