INDIANAPOLIS — Preliminary results from a new state study about the impact of COVID-19 on Indiana suggest as many as 186,000 Hoosiers were actively or previously infected as of May 1.
The study, conducted by Indiana University and the Indiana State Department of Health, show a general population prevalence of about 2.8 percent of the state's population.
"What we knew through conventional detection methods — testing symptomatic people and those at high-risk for COVID-19 — was just the tip of the iceberg," Nir Menachemi, lead scientist of the study and a professor and Fairbanks Endowed Chair in the Indiana University Richard M. Fairbanks School of Public Health at IUPUI, said. "Now we're trying to figure out how big that iceberg actually is."
Paul Halverson, founding dean of the Fairbanks School of Public Health, said continued testing will answer the question and assist with fighting the spread of COVID-19.
"Ideally, we would test every Hoosier," Halverson said. "But the next best thing is random sample testing, a scientific approach that allows us to confidently assess how COVID-19 has spread in Indiana, without having to test everyone."
In the first phase of the study, researchers tested more than 4,600 Hoosiers between April 25 and May 1 for viral infections and antibodies of SARS-CoV-2, the novel coronavirus that causes COVID-19. The number includes more than 3,600 people who were randomly selected and an additional 900 volunteers recruited through outreach to the African-American and Hispanic communities to more accurately represent state demographics.
According to the study, researchers found that during the last week in April 1.7 percent of participants tested positive for the novel coronavirus and an additional 1.1 percent tested positive for antibodies. The estimated prevalence of the virus in the state was 2.8 percent — 186,000 Hoosiers — who were actively or previously infected as of May 1, Menachemi said.
As of the same date, the state's testing showed about 17,000 cumulative cases, not including deaths, suggesting only about one out of every 11 true infections were identified by tests focused on symptomatic or high-risk people.
The latest confirmed cases from the state health department is 25,473 with 1,482 deaths, according to numbers released Wednesday.
Researchers said having a reliable estimate of the number of people infected also enables scientists to calculate much sought-after but otherwise unknown rates like the infection-fatality rate, which represents the proportion of all those infected who have died, as opposed to the case-fatality rate, which focused mostly on symptomatic and high-risk cases.
IUPUI scientists estimate the infection-fatality rate for the novel coronavirus in Indiana to be 0.58 percent, making it almost six times more deadly than the seasonal flu, which has an infection-fatality rate of 0.1, according to the U.S. Centers for Disease Control and Prevention.
Menachemi said the research team also found that almost 45 percent of people who tested positive for active viral infection reported no symptoms at all.
The study also identified that certain communities have been affected by COVID-19 more than others. Analysis of the random sample suggests that Hispanics, African-Americans and other races including those who identify as bi-racial have higher positive rates of the virus.
"This was confirmed with data from the targeted outreach that allowed us to gain additional participants from these communities — further strengthening the evidence in support of this disparity," Menachemi said.
"We're so grateful for this work. It's an important snapshot in time of what is happening in our state, and future testing phases will bolster our knowledge," Dr. Kris Box, Indiana State Health Commissioner, said. "These initial results will help guide us in our efforts to make decisions about how we move forward in Indiana and better position resources."
Menachemi said the state's social distancing policies seem to have played a role in curbing the spread of the virus. Study participants who reported living with a person in their household who was positive for the virus were nine times more likely to test positive themselves. Coupled with the state's 2.8 percent general population prevalence, seems to imply Indiana has been able to contain a large number of infections to within households, he said.
"By slowing the spread of the virus, we now have bought some time to determine the best way forward," Menachemi said. "However, it is important to stress that the vast majority of the people in Indiana have not been infected and represent the minimum pool of still susceptible individuals. Therefore, as we slowly phase back and open the economy, we need to be extra vigilant with any and all safety precautions so that we do not lose the ground that we gained by hunkering down."
More phases of testing are planned for early June, October and April 2021.