The authors, from the Department of Health Management and Policy at the University of Iowa, based their assessment on an analysis of confirmed cases of the disease caused by the new coronavirus, SARS-CoV-2, in the region along the Illinois-Iowa border.
Illinois implemented a stay-at-home measure for social distancing on March 21. Conversely, Iowa took a more phased approach before finally closing all "non-essential" businesses -- exceptions include supermarkets, pharmacies and, notably, food processing facilities, among others -- on April 2.
"There are differences in case spread that are consistent with other national studies of the effects of social distancing," study co-author George Wehby, a professor of public health at the University of Iowa, told UPI.
"Collectively, the building evidence is pointing to a role for these measures, and the earlier they are adopted, the more effective they appear to be, while the piece-wise adoption used in places like Iowa may not be as effective," he said.
Iowa is one of only five states that have not issued stay-at-home orders, which are designed to limit movement and social interactions to contain the spread of the virus. Arkansas, Nebraska, and North and South Dakota are the others.
To date, Iowa has reported just over 13,000 confirmed cases of COVID-19, while Illinois has nearly 85,000, according to the latest figures from Johns Hopkins University. However, roughly 95 percent of the confirmed cases in Illinois are in the northeastern part of the state, with only a small percentage in the more rural counties near the Iowa border.
For their analysis, Wehby and his colleague Wei Lyu compared COVID-19 cases in eight border counties in Iowa with cases in seven border counties in Illinois, where a stay-at-home order was in place.
The counties included in the analysis were Clinton, Des Moines, Dubuque, Jackson, Lee, Louisa, Muscatine and Scott in Iowa, and Carroll, Hancock, Henderson, Jo Daviess, Mercer, Rock Island and Whiteside in Illinois.
The researchers found that, before Illinois' stay-at-home order, the Iowa counties had a cumulative case rate of 0.024 per 10,000 residents compared to 0.026 per 10,000 residents in the Illinois counties. However, within 30 days of Illinois issuing its directive, the Iowa counties had 4.71 more cases per 10,000 residents than their Illinois counterparts.
Based on these findings, Wehby and Lyu estimate that as many as 217 "excess cases" existed in the border Iowa counties, which represents more than 30 percent of the 716 total cases there through April 21. These excess cases also could be due to Illinois testing about 50 percent more people than Iowa by that date.
Wehby noted the findings indicate that stay-at-home measures "should be part of the toolkit state governments should consider" to contain infectious disease outbreaks like COVID-19.
"We don't really know which component of the various social distancing measures put in place is most helpful," Dr. Michael Mina, assistant professor of epidemiology at Harvard T.H. Chan School of Public Health, said during a conference call with reporters on Friday.
"We sort of did everything at once," added Mina, who was not part of the Iowa study. "We stopped work, we stopped transit, we stayed at home.
"As states open up differently, I'd like to see departments of public health track how reopening affects cases and understand which are the most important features for containing spread."