Fig 4.

Ratio of new to cumulative cases among detained persons and staff in Cook County Jail compared to Chicago—IL, March 1-April 30, 2020.

Ratios of new cases to cumulative cases were calculated for each week of the study period among detained persons, staff, and residents of Chicago and plotted on a logarithmic scale to show outbreak trajectories. For staff, all symptomatic persons with validated molecular test results from the Illinois National Notifiable Disease Surveillance System (I-NEDSS) were included using date of onset as the referent time point; all asymptomatic and symptomatic detained persons testing PCR-positive were included using date of symptom onset or specimen collection as the referent time point. Data for all persons residing in the state of Illinois meeting the case definition for confirmed SARS-CoV-2 infection were extracted from the I-NEDSS system and included using the date of specimen collection.

Each node represents 1 week of the study period; the highest number of total cases were identified in the jail the week of April 5th and fell thereafter. The initial doubling times for Chicago, staff, and detained persons were 2.22, 2.15, and 2.1 days, respectively, represented by the increasing slope prior to peak for each population.