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Louisville Study Finds Higher COVID-19 Exposure Rates Than Expected

Centers for Disease Control and Prevention

A study of COVID-19 antibodies in Louisville residents has found higher exposure rates than researchers expected.

The study conducted by the University of Louisville’s Christina Lee Brown Envirome Institute tested 2,237 Jefferson County adults between June 10 and 19; the participants volunteered after either receiving a postcard in the mail or hearing about the study. 10% of them were non-white. Researchers found that at least 0.05% of the people were infected with COVID-19 at the time they were tested, and the blood of nearly 4% had measurable levels of antibodies, which researchers believe means they have been exposed to the coronavirus.
That suggests four to six times more people than previously thought may have been exposed to the virus.

“These results are important because they, for the first time, give us sort of an accurate picture of how widespread the viral infection has been in the community,” said Envirome Institute Director Aruni Bhatnagar. “And if we can extrapolate these results to the general population [it could mean] as many as 20,000 people have been exposed to the virus, starting in late January. This is much, much higher than the 3,800 cases that the city reported by the end of June.”

Bhatnagar said the data also provides a clearer picture of the mortality rate from the coronavirus. Estimates of mortality have varied widely from 0.5% to 15%, but the number has been difficult to nail down because some people with COVID-19 never show symptoms, and thus are never tested or diagnosed with the virus. Considering this new exposure data with the number of deaths city officials had reported by the end of June — 209 — Bhatnagar said this indicates the mortality rate has been around 1.3% in Jefferson County.

Researchers drew participants from all around the city, but researchers found that the highest rates of infection were in west Louisville neighborhoods.

“[West Louisville rates are] much higher than other parts of the city, and it would represent the highest clusters of people exposed,” said Rachel Keith, a U of L assistant professor of environmental medicine who conducted the study.  “We believe that the prevalence of exposure is twice as high in our non-white participants as our white participants as well.”

One of the factors behind those geographic disparities is the number of people who were exposed to COVID-19 while working through the pandemic, according to Metro Louisville Chief Health Strategist Sarah Moyer.

“We know that back in March, April, May when the majority of our city was able to be at home and practicing social distancing…a higher percentage of people from those neighborhoods were the ones in essential jobs and working,” she said. “So that would be my best educated guess as to why those numbers are higher.”

This is the second phase of the Co-Immunity Project; the first phase studied health care workers. U of L officials say the research will continue through “several more cycles”.

The next phase will start in September and will repeat community-wide testing across the county.

Erica Peterson is WFPL's Director of News and Programming.