It was a cough so slight that it hardly qualified as a cough.

Kari Houser had spent the day raking leaves and clearing brush from the yard. After returning to the house late in the afternoon, the mother of two was feeling flush, achy and a "little funny." 

Her temperature was a slightly elevated 99.6, but hardly off the charts. Even so, Houser called a Mayo Clinic triage nurse who recommended that she be tested for COVID-19.

When Mayo later called with the result, she knew it had come back positive. 

"They don't call if you're negative," Houser said. 

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Last Thursday, a month later, a fully recovered Houser was among the first to donate plasma in Rochester to a national convalescent plasma project headed and coordinated by Mayo Clinic.

Plasma donors are key to a therapy with the potential to save tens of thousands of lives with the life-giving, antibody-rich blood. 

When the Food and Drug Administration tapped Mayo to lead the National COVID-19 Convalescent Plasma Project earlier this month, the expectation was that 50 to 100 hospitals would enroll in the study and perhaps 500 to 1,000 patients be treated with plasma. 

Those expectations were soon shattered by a surge of interest. As of last Friday, 1,485 hospitals, 1,815 doctors and 1,280 patients have enrolled, said Dr. Scott Wright, a Mayo cardiologist and clinical researcher -- with the numbers expected to grow.

Of the 1,280 patients who joined the study, only about a quarter of them have received plasma or have had plasma ordered for them, Wright said. 

"You can do the math. We have almost 900 who don't have access to plasma right now, because we don't have enough donors or enough delivery of available plasma to all the hospitals," Wright said. 

"We need more people to donate. We need more people to hear about this," Wright said. 

Blood plasma therapy is a century-old technique that was used on patients during the 1918 flu pandemic.

The therapy is rooted in the body's disease-fighting ability. In the current situation, people who have been infected with coronavirus generate antibodies within days of being infected. Scientists are hoping that those antibodies taken from a recovered COVID-19 patient can be transferred to boost the immunity of a sick person.

A 48-year-old Onalaska, Wis., resident who works in administration at La Crosse-Mayo Clinic Health System, Houser isn't certain how she got the disease. A county health worker speculated that her infection may have occurred during a family trip to Cedarburg, Wis., north of Milwaukee, to watch her son play hockey. 

"We stood by ourselves," Houser said. "But we could have touched door handles. We went to a sandwich shop for lunch. It could have been there at the table or the person who was working there. There's just no way of knowing at what point" she picked up the virus.

After testing positive, Houser, her husband, son, daughter and daughter's boyfriend were quarantined in the Onalaska home for two weeks. 

Houser has been a blood donor for two decades, so plasma donation seemed natural to her.

Although her family and daughter's boyfriend were all presumed to be infected, most have not been tested for COVID-19 because they don't meet the criteria to be tested.

Houser did because she works in health care. Even though others in her family may have the antibodies that doctors are looking for, they so far have not able to donate. 

Houser made her donation in the Hilton Building in Rochester. She was surprised to learn that she was only the fourth plasma donor at Mayo. She hopes her example inspires others to donate. 

"Certainly, the plasma is highly valuable to people who are at risk or newly diagnosed with the disease," she said. 

To donate, individuals must have a verified COVID-19 diagnosis as well as be either symptom free for at least 28 days or symptom free for at least 14 days and have a negative COVID-19 test result. 

To find a place to donate plasma, go to: aabb.org/tm/donation/Pages/Blood-Ban-Locator.aspx.