How Did the Nosocomial Outbreak of COVID-19 Occur, and How Was it Contained?

In April 2020, we experienced a nosocomial outbreak of COVID-19. As a result of the outbreak, a total of 36 people were laboratory-confirmed to be infected, including 7 inpatients and 29 staff members. A total of 354 PCR tests were conducted on patients and staff, and 349 staff members were placed on self-monitoring at home. The following four routes of infection were estimated: 1) transmission from known infected patients to staff, 2) transmission from patients who have not yet been diagnosed with COVID-19 to staff, 3) transmission from staff who have been contracted with COVID-19 in 1) to patients, 4) transmission among staff, and 5) transmission from an environment contaminated with SARS-CoV-2 to staff. After the outbreak was confirmed, the area was red-zoned, and the following measures were taken: 1) red-zoning to reduce the number of donning and doffing of personal protective equipment, 2) mandating infected patients to use surgical masks all the time, and 3) universal masking of staff and patients in the hospital. The criteria for entering the critical care unit were also developed. As a result of these measures, the outbreak was successfully contained, and we were able to maintain cluster-free environment as of this writing.