Clustering and multiple-spreading events of nosocomial severe acute respiratory syndrome coronavirus 2 infection

Abstract

Background There is growing evidence that super-spreading events (SSEs) and multiple-spreading events (MSEs) are a characteristic feature of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, data regarding the possibility of SSEs or MSEs in healthcare settings are limited. Methods This study was performed at a tertiary care hospital in Korea. We analysed the nosocomial COVID-19 cases that occurred in healthcare workers and inpatients and their caregivers between January and 20 th December 2020. Cases with two to four secondary cases were defined as MSEs and those with five or more secondary cases as SSEs. Findings We identified 21 nosocomial events (single-case events, n = 12 [57%]; MSE + SSE, n = 9 [43%]) involving 65 individuals with COVID-19. Of these 65 individuals, 21 (32%) were infectors. The infectors tended to have a longer duration between symptom onset and diagnostic confirmation than did the non-infectors (median 2 days vs. 0 days, P = 0.08). Importantly, 12 (18%) individuals were responsible for MSEs and 1 (2%) for an SSE, which collectively generated 35 (54%) secondary cases. Conclusion In a hospital with thorough infection control measures, approximately 70% of the nosocomial cases of COVID-19 did not generate secondary cases, and one-fifth of the infectors were responsible for SSEs and MSEs, which accounted for approximately half of the total cases. Early case identification, isolation, and extensive contact tracing are important for the prevention of transmission and SSEs.

Risk of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Transmission Among Healthcare Workers Dining in Hospital Staff Cafeterias

“…Additionally, some may argue that secondary cases in the study could have acquired infection from other individuals rather than from the presumed index cases because we did not perform whole-genome sequencing (WGS) to confirm infection sources. However, as shown in our previous study, 5 WGS was not helpful for identifying infection sources when there were no epidemiologic links. Indeed, we did not find any epidemiologic links other than contact with index in our thorough re-investigation.…”

“…Therefore, we believe that SARS-CoV-2 exposure in places other than the staff cafeterias in these three HCWs is unlikely considering the extensive epidemiologic investigations performed by our infection control team with the help of government epidemiologic investigators and the relatively low community transmission level during the study period in South Korea (low or moderate transmission: < 10 or 10–49 new cases per 100,000 persons in the week). 5 Third, transmission risk did not differ according to levels of acquaintance between index and contacts. This may have been due to the small sample size.…”

“…We notified individuals who were exposed inside or outside the cafeterias, and they underwent testing for SARS-CoV-2. As previously reported, 5 6 we also performed contact tracing outside the cafeteria. The exposure to the COVID-19 patients included close and non-close contacts, which were defined as previously reported.…”

“…Whenever a case of coronavirus disease 2019 (COVID-19) was detected, we performed contact tracing, as previously reported. 5 From January 2020 through September 2021, we analyzed the risk of COVID-19 transmission, in hospital staff cafeterias, to staff members seated close to individuals who would later test positive for SARS-CoV-2 infection (index). We reviewed closed-circuit television (CCTV) footage and radio-frequency identification (RFID) tagging in the cafeterias to identify contacts.…”

Experience of a COVID-19 outbreak response in a general hospital in Gyeonggi Province, Korea

“…The first COVID-19 case in Korea, which was confirmed on January 20, 2020, was imported from Wuhan, China [ 2 ]. During the COVID-19 pandemic, Korea has experienced several COVID-19 outbreaks that involved hospitals [ 4 - 7 ]. Clusters related to general hospitals are riskier than other clusters because these outbreaks not only overburden the regional healthcare delivery system, but also increase the possibility of community transmission [ 6 , 8 , 9 ].…”