Outbreak investigation of COVID-19 in a central region prison, May–June 2023

Abstract

ฺBackground: On May 18, 2023, the Communicable Disease Control Division, Ang Thong Provincial Public Health Office, received a report of clustered suspected COVID-19 cases in a prison in the central region of Thailand. An outbreak investigation and disease control measures were initiated to confirm the diagnosis, establish the outbreak's occurrence, identify contributing factors, and formulate disease control strategies.

Methods: A descriptive epidemiological study was conducted through active case finding, using case definitions based on guidelines from the Bureau of Epidemiology. Surveillance data, prison medical records, environmental conditions, laboratory results, structured interviews with inmates and prison staff were reviewed. A case-control design was conducted to identify factors associated with the outbreak between May 10 and June 1, 2023.

Results: A total of 239 cases were identified, comprising 50 suspected cases, 176 probable cases, 13 confirmed cases, involving 180 inmates and 9 staff members, resulting in an attack rate of 17.15%. No fatalities occurred. Most cases were male (93.12%). The first case developed symptoms on May 10, 2023, with the last case identified on May 21, 2023. Whole genome sequencing from two male inmates and one staff member revealed the Omicron variant B.1.1.529 sub-lineage XBB.1.5. Significant risk factors for spreading included sharing drinking cups potentially contaminated with COVID-19 (AOR = 4.10, 95% CI: 1.43–11.73), visiting high-density areas such as the dining hall and sports field (AOR = 7.43, 95% CI: 1.98–27.89), history of contact with COVID-19 patients (AOR = 2.88, 95% CI: 1.42–5.84), and residing in the dormitory where the first case was identified (AOR = 2.59, 95% CI: 1.20–5.59). A protective factor identified was the use of the prison welfare shop (AOR = 0.35, 95% CI: 0.18–0.70).

Conclusion: The investigation confirmed a propagated outbreak of COVID-19 in a prison in the central region, likely initiated by an inmate who entered the closed prison system after initially tested negative by rapid antigen test. Risk factors contributing to the spread included high-density gatherings, shared use of drinking cups, direct contact with infected individuals, and dormitory cohabitation with the first case. Protective measures included utilization of the prison welfare shop. The implementation of strict control measures, staff training, enhanced surveillance systems, promotion of personal hygiene, and cooperation among inmates and prison staff successfully contained the outbreak.