COVID-19 outbreak investigation and response in a penitentiary setting: the experience of a prison in Italy, February to April 2020.

Prisons are high-risk settings for COVID-19 and present specific challenges for prevention and control. We describe a COVID-19 outbreak in a large prison in Milan between 20 February and 30 April 2020. We performed a retrospective analysis of routine data collected during the COVID-19 emergency in prison. We analysed the spatial distribution of cases and calculated global and specific attack rates (AR). We assessed prevention and control measures. By 30 April 2020, 57 confirmed COVID-19 cases and 66 clinically probable cases were recorded among a population of 1,480. Global AR was 8.3%. The index case was a custodial officer. Two clusters were detected among custodial staff and healthcare workers. On 31 March, a confirmed case was identified among detained individuals. COVID-19 spread by physical proximity or among subgroups with cultural affinity, resulting in a cluster of 22 confirmed cases. Following index case identification, specific measures were taken including creation of a multidisciplinary task-force, increasing diagnostic capacity, contact tracing and dedicated isolation areas. Expanded use of personal protective equipment, environmental disinfection and health promotion activities were also implemented. Outbreaks of COVID-19 in prison require heightened attention and stringent comprehensive measures.