Indiana sampling study

The Centers for Disease Control and Prevention have published results from the first phase of Indiana's statewide random sampling study of COVID-19 conducted back in April.

INDIANAPOLIS — The Centers for Disease Control and Prevention published the initial findings from the Indiana University Richard M. Fairbanks School of Public Health at IUPUI, the nation’s first statewide random sampling study to look for prevalence of COVID-19.

The study, which was launched in the early days of Indiana’s pandemic response and led by Dr. Nir Menachemi, the Fairbanks Endowed Chair of the school of health, showed at the time of the first round of testing back in April that COVID-19 had impacted only about 2.8% of the population.

The results of the first phase of that study, which were released in a preliminary capacity to the public back on May 13, are somewhat old news now — the Fairbanks study released a second phase of results to the public on June 17 — but they have been published by the CDC as the first example of a statewide effort to measure the true scope of COVID-19.

In the early days of the pandemic, and even to some extent today, knowing the full reach of COVID-19 was difficult.

Due to severe limitations in the capacity of testing, positive test results were only capturing a fraction of actual cases as even people who were sick with COVID-like symptoms were not being tested unless their cases were serious.

Beyond that, health officials have known that many people carry COVID-19 either with very minor symptoms or no symptoms at all, making it difficult to know for sure who did or didn’t have the virus.

The Fairbanks study was designed to take a random sample representative of Indiana’s population and test both for active infection as well as antibody testing to look for signs of people who may have had a prior infection without knowing it.

“Because we cannot test everyone, random sample testing allows us to confidently evaluate the spread of COVID-19 in Indiana,” said Menachemi, in an Indiana State Department of Health release on Tuesday. “The results of this study have furthered our scientific knowledge of COVID-19 and contributed valuable information that influenced complex statewide decision-making.”

That first round of results from testing done in April showed that, among a sample size of about 4,600 Hoosiers, 1.7% showed an active infection and 1.1% had antibodies showing a previous infection.

At the time, those numbers showed that current testing efforts had only identified about 1 in every 11 actual cases.

More importantly, the Fairbanks study showed that approximately 44% of people who had an active infection had no symptoms. That number was later supported by the second round of testing where a near-same percentage of people with current infection showed no symptoms.

With that estimation of actual impact of the virus, the study authors were also able to estimated a true mortality rate of the virus at that point, showing about 0.58% death rate, approximately six times that of typical seasonal influenza.

“The estimated infection-fatality rate was 0.58%, or approximately six times the 0.1% mortality rate for influenza. This fatality rate is lower than the infection-fatality rate of 1.3 observed on a cruise ship but consistent with an extrapolated infection-fatality rate in China of 0.66% derived from a nonrandom sample of persons repatriated to their countries from China after the outbreak,” the study states.

The initial phase of the study also revealed some other interesting data points.

People who were living with someone who tested positive were 15 times more likely to contract the infection.

That data point was used to reinforce that social distancing efforts that reduce proximity and exposure times are likely to be effective at reducing transmission of the virus.

Of the asymptomatic patients identified in the study, about 60% were male compared to just 24.5% of females.

The Fairbanks study also showed that infections were far more prevalent among Hispanic participants at 8.32% than other demographic groups at just 2.29%.

The CDC’s evaluation of the study suggests that the results reinforce the need for ongoing preventative measures for COVID-19, as large swaths of the population still have not been exposed to the virus.

“The number of reported cases represents an estimated one of 10 infections. Given that many persons in Indiana remain susceptible, adherence to evidence-based public health mitigation measures (e.g., social distancing, consistent and correct use of face coverings, and hand hygiene) is needed to reduce surge in hospitalizations and prevent morbidity and mortality from COVID-19,” the CDC entry states.

The entry on the CDC website and detailed results from the study can be found at bit.ly/2OL5te4.

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