Jails infected by COVID-19 pose a threat not only to prisoners inside but also to people in nearby communities, researchers reported in the journal Health Affairs Monday.

Data suggests more than 4,700 cases of COVID-19 in Illinois up through April 19 were associated with 2,129 individuals going through the Cook County Jail in March, researchers from Harvard University said.

The prison may be linked with 15.7 percent of all confirmed COVID-19 cases in Illinois and 15.9 percent in Chicago, they said.