key: cord-1011783-os14w2t6
authors: Jung, Jiwon; Lim, So Yun; Lee, Jungmin; Bae, Seongman; Lim, Young-Ju; Hong, Min Jee; Kwak, Sun Hee; Kim, Eun Ok; Sung, Heungsup; Kim, Mi-Na; Bae, Joon-Yong; Park, Man-Seong; Kim, Sung-Han
title: Clustering and multiple-spreading events of nosocomial severe acute respiratory syndrome coronavirus 2 infection
date: 2021-08-25
journal: J Hosp Infect
DOI: 10.1016/j.jhin.2021.06.012
sha: 369b29418811fdf25a25a2ad8431c041ffa2eb9a
doc_id: 1011783
cord_uid: os14w2t6

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.

The World Health Organization declared the outbreak of coronavirus disease 19) as a pandemic on 11 th March 2020. As of 19 th December 2020, more than 76.8 million 72 cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection had with a total of 55 wards, including 14 wards in the West building (6 th floor-12 th floor), 24 94 wards in the East building (7 th floor-18 th floor), and 17 wards in the New building (6 th floor-95 15 th floor; Figure 1 ). All wards have single-occupancy rooms, two-patient rooms, and six-96 patient rooms. In addition, one ward was designated as an isolation ward for cohorting 97 patients with suspected COVID-19 or patients who had close contact with a patient with 98 confirmed COVID-19 or epidemiologic risk factors for COVID-19. 99 Since February 2020, we have performed symptom-and epidemiologic risk-based 100 screenings in our hospital as a whole (i.e. outpatient clinic, emergency room, pre-admission, 101 and inpatient); since 29 th April 2020, we have implemented a universal pre-admission 102 screening policy for SARS-CoV-2 using RT-PCR in nasopharyngeal swab specimens, which 103 was applied to individuals without symptoms associated with COVID-19, epidemiologic risk 104 factors, or links with recent outbreaks in the community or hospitals. Caregivers were defined as the individuals who provide care to inpatients, which included 179 family members or hired professional caregivers. HCWs included physicians, nurses, 180 emergency medical personnel, dental professionals and students, medical and nursing 181 students, laboratory technicians, pharmacists, hospital volunteers, and administrative staff.

relationship; thus, we performed WGS analysis. Unexpectedly, the sequences were different 239 between them. However, the patient in E13F (ward 133) had the same sequences as the N11F 240 cluster (no epidemiologic relationship, group A in the WGS analysis), and the HCW in E13F 241 had the same sequences as the E7F cluster (group B in the WGS analysis). In addition, we 242 found that the E7F cluster had the same sequences as the N9F cluster (group B). Therefore, 243 we re-investigated the epidemiologic association; however, there were no epidemiologic links 244 or contacts found using the CCTV footage. There was one exception wherein the caregiver in We later found that the air inlet and outlet in the ceiling of the room were well functioning.

In this study, we found that approximately 70% of the individuals with COVID-19 did 

We performed WGS when diagnosis of the non-close contacts who had possible 288 temporal or spatial relationships with the index patients was confirmed by SARS-CoV-2 PCR 289 testing. Notably, we found one transmission case that was consolidated in the WGS analysis. When there were no epidemiologic links, we found that WGS was not helpful in 300 identifying the unexpected epidemiologic links even by re-investigating the possible links 301 through CCTV footage tracing and interview. Although the same sequence was shown in the 302 WGS analysis between the patient and caregiver who had contact in the outdoor waiting 303 room while both being masked, it was difficult to determine whether the transmission 304 actually occurred in the outdoor waiting room without face-to-face contact between these two 305 appropriately masked individuals. In addition, we did not find any epidemiologic links in our 306 thorough re-investigation between the different clusters and wards with the same sequences.

were simultaneously imported to our hospital, as shown in the phylogenetic tree in Figure 4 . 

Heterogeneity in virus shedding among 366 medically-attended influenza A virus infections

Superspreading SARS events, Bijing