La Crosse County health officials reported Tuesday that a resident has been reinfected with COVID-19, though scientists studying the virus have yet to report a case that was confirmed to be a reinfection, and not a flare-up of a previous infection.

According to a Facebook post from the La Crosse County Health Department, the person first tested positive for COVID-19 more than three months ago.

The Centers for Disease Control and Preventionon July 22 said there had been no confirmed cases of COVID-19 reinfection, but scientists continue to investigate the possibility.

The La Crosse County Health Department was not immediately available for comment Tuesday evening, but health officials did respond to questions earlierTuesday on the department's Facebook page.

In response to a Facebook comment askingwhether the infection could possibly be "one long case," the health department said it was considering the case a reinfection and cited guidance from the CDC: "If a positive test occurs more than 3 months after a persons symptom onset, clinicians and public health authorities should consider the possibility of reinfection."

The patient's symptoms "were not the same the second time," the health department said in response to another question,thoughhealth officials did not share what those symptoms are.

In a July 22 story in The New York Times, scientists said it would be extremely rare for someone to become reinfected with COVID-19, but not impossible.

And people who've been infected with related coronaviruses "appear to become susceptible again at around 90 days after onset ofinfection," according to the CDC.

A study published in the New England Journal of Medicine suggests the antibodies produced by the immune system to fight COVID-19 may only last a few months in people with mild cases. But once infected, the immune system remembers how to make fresh antibodies if needed, according to a story byThe Associated Press.

There is also a growing recognition among scientists and doctors that it's possible for the virus to lay dormant for months and then flare up again insome patients.

It is difficult to prove beyond a reasonable doubt that a person has been reinfected with COVID-19, said Dr. Nasia Safdar,who studies infectious disease at the University of Wisconsin-Madison and is medical director of infection control at UW Health.

Certain conditions have to be met to prove a reinfection, Safdar said. A person first has to recover from the original infection and then be infected with a strain of the virus that is either different from what they had before or that can be "cultured," meaning grown in a lab and proven to be a live, viable virus "and not just a persistent presence" of the original COVID-19 infection.

Safdar said most labs are not equipped to culture for COVID-19 because its hazardous.

In the absence of that, the best you can do is have some sort of criteria that if a certain amount of time has elapsed and somebody comes up with still a (positive test),it may be reinfection."

But that doesn't necessarily prove a reinfection, she said, because scientists have learned that people still test positive for the coronavirus "several weeks after the first infection."

Cases that have been reported as "reinfections" could instead be a person's first encounter with the virus, after a person's initial test was a false positive.

La Crosse isn't the only county in the U.S. to report a reinfection. Also Tuesday, Todd County in Kentucky reported that a single patient was counted asa reinfectionbecause more than 90 days had passed between positive tests.

As of Tuesday, there have been 844 confirmed cases of COVID-19 in La Crosse County. Four people are hospitalized and one person has died.

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Contact Natalie Brophy at (715) 216-5452 or nbrophy@gannett.com. Followher on Twitter @brophy_natalie.

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A Wisconsin county says a resident was 'reinfected' with COVID-19, though scientists have no proof that can happen yet - Appleton Post Crescent