Rapid Spread of SARS-CoV-2 in a State Prison After Introduction by Newly Transferred Incarcerated Persons — Wisconsin, August 14–October 22, 2020

Investigation and Findings

Prison A is a medium-security state prison in Wisconsin with 300–350 staff members and a maximum capacity of 1,192 men housed in 15 units. Except for one unit (a restrictive housing unit with locked cells), all units have shared lavatories and common areas, including one 150-person dormitory-style unit with conjoined sleeping and common areas. Before the outbreak, prison A implemented multiple mitigation measures, including mandatory mask wearing for staff members and incarcerated persons.^† During August 17–19, 2020, members of a group of incarcerated men transferred from a Wisconsin central intake facility on August 13 were tested for SARS-CoV-2 by real-time reverse transcription–polymerase chain reaction (RT-PCR)^§ in accordance with routine intake procedures^¶; six received positive test results and were immediately isolated. Before testing, the new intake group was housed with other incarcerated persons, most of whom were recent transfers, in the intake unit. On August 24, testing of incarcerated persons in the intake unit identified six additional cases in incarcerated persons, who were immediately isolated. On August 25, intake processing was suspended, the intake unit was locked down,** and the remaining persons in the unit started a 14-day group quarantine. After receiving the test results from facilitywide testing on September 1, incarcerated persons with COVID-19 were moved to the intake unit, which potentially exposed quarantined persons to SARS-CoV-2. The 14-day quarantine that started on August 25 was not restarted after the potential exposure to persons with COVID-19. Mass (facilitywide) and targeted (selected units) testing was conducted on September 1, 14, and 23–24, and detected rapid spread; the percentage of positive test results among incarcerated persons was 2.4% on September 1 and increased to 46.2% on September 23.

After September 14 test results identified 86 cases of COVID-19 among incarcerated persons, the facility implemented a modified lockdown, restricting movement of incarcerated persons across units and shutting down common areas; however, staff members continued to rotate throughout the facility because of staffing shortages and scheduling policies. By September 22, the facility was unable to medically isolate or quarantine incarcerated persons because of limited space. On September 28, the Wisconsin DHS and Wisconsin Department of Corrections contacted CDC to request assistance in investigating the outbreak.

A COVID-19 case was defined as a positive SARS-CoV-2 test result^†† received by any incarcerated person or staff member at prison A during August 14–October 22, 2020. Voluntary testing was offered to incarcerated persons during mass or targeted testing, routine intake screening (on postintake days 4 or 5), or when symptoms were reported. Staff members were tested at the first two mass testing events and were instructed to report receipt of positive test results from outside testing. Epidemiologic data were extracted from prison-managed documents and the Wisconsin Electronic Disease Surveillance System. Attack rates were calculated using population estimates communicated by prison A. A heat map was created to show the percentage of new cases across units and testing events, assuming maximum capacity. This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy.^§§

On September 1, a total of 8 days after cases were identified on the intake unit, facilitywide testing identified cases in six of 15 units (Supplementary Table, https://stacks.cdc.gov/view/cdc/104507). Twenty-two days later (September 23), cases were identified across all 15 units, with infections in three units progressing from zero cases to attack rates ranging from 66.2% to 84.6% during that period. During August 14–October 22, a total of 869 (79.4%) of 1,095 incarcerated persons (median age = 36 years, range = 18–83 years) and 69 (22.6%) of 305 staff members (median age = 44 years, range = 23–77 years) received positive SARS-CoV-2 test results (Figure 1). Among 869 incarcerated persons with COVID-19, 118 (14%) were infected in the dormitory-style unit (unit 15). Six incarcerated persons were hospitalized (median age = 58 years, range = 33–69 years), one of whom, a man aged 56 years, died. Mass or targeted testing identified 95.4% (829 of 869) of cases in incarcerated persons and 42.0% (29 of 69) of cases in staff members. In the 14 days before reporting onset of COVID-19 symptoms or receiving positive SARS-CoV-2 test results, 71 (8.2%) incarcerated persons transferred units, and 27 (39.1%) staff members were assigned to more than one unit.