Coronavirus Disease 2019 Clusters Research Articles

A questionnaire survey of infection control measures during the coronavirus infectious disease 2019 pandemic era

ObjectiveTo clarify the infection control measures required in the event of a new infectious disease outbreak, we conducted a questionnaire survey on the infection control measures implemented against coronavirus disease 2019 (COVID-19). MethodsAn invitation to participate in this survey was sent to the heads of 2689 facilities affiliated with the members of the Japanese Society for Infection Prevention and Control in February 2023, requesting responses to the online survey using Google Forms by March 2023. ResultsSix hundred and forty-five facilities, including 20 clinics and 625 hospitals, participated in the survey. This survey revealed that various infection control measures were implemented, including universal masking in the non-COVID-19 ward (96.5 %), screening tests for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on scheduled admission (89.0 %), SARS-CoV-2 tests (98.7 %), and isolation in private rooms (76.5 %) for inpatients with fever. However, nosocomial infections and clusters of COVID-19 occurred in 94.4 % and 90.9 % of cases during the investigation period, respectively. One of the reasons for these results is that healthcare personnel (HCP) and patients were common index cases of nosocomial infections, and the most common cause of clusters was the work of symptomatic HCPs. These results suggest that HCPs should understand that they can be index cases or spreaders. On the other hand, the most common support from external facilities was healthcare centers, followed by physicians or nurses from other hospitals. ConclusionIn response to the emergence of infections, it is important to consider implementing infection control measures for HCPs and patients.

Risk Factors for COVID-19 Cluster Infection in Hospitalized Patients.

Introduction In Japan, in the seventh wave of coronavirus disease 2019 (COVID-19) from July 2022 to September 2022, followed by the eighth wave of COVID-19 from November 2022 to January 2023, nosocomial clusters became more frequent in many healthcare facilities. If a cluster occurs in a hospital, the restrictions on general healthcare and the impact on hospital management, as well as the impact on community healthcare, are enormous. We analyzed the risk factors for COVID-19 cluster infection in hospitalized patients. Methods We retrospectively collected cases of COVID-19 infection among hospitalized patients in the seventh and eighth waves. The occurrence of a COVID-19 patient in a hospitalized patient was defined as one event. Results A total of 40 events were observed in the seventh and eighth waves. There were 17 events that developed into clusters. The following factors showed a significant association with cluster infection in a univariate analysis: "seventh wave," "originated from healthcare worker," and "initial examination according to contact list." The multivariate analysis revealed that "originated from healthcare worker" was independently associated with cluster infection. Conclusion Preventing the development of COVID-19 clusters is very important for nosocomial infection control. Our study suggests that COVID-19 infection in a healthcare worker is a risk factor for the development of a cluster. When healthcare workers are infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), it is often due to household transmission. Measures against household transmissions are important to prevent infection among healthcare workers.

The impact of implementing barrier curtain placement in reducing nosocomial COVID-19 clusters at a tertiary care facility

Abstract Objective: This study aimed to asses the impact of a physical barrier-based infection prevention and control (IPC) intervention in patient wards at a tertiary care center on patient-to-patient coronavirus disease-2019 (COVID-19) transmission and cluster formation. Materials and Methods: A quasi-experimental study was conducted at a 1300-bedded South Indian tertiary care center. Barrier curtains were deployed between ward beds, accompanied by a social interaction protocol, at eight locations, each containing eleven 4-bedded cubicles accommodating 44 patient beds. A surveillance team daily audited adherence to mask usage, barrier curtains, and the social interaction protocol using a predefined checklist. An effective implementation hybrid design was employed to evaluate clinical impact (cluster formation) and implementation effectiveness (adherence to interventions) between the pre-implementation and post-implementation phases. Results: During the pre-implementation and post-implementation periods, 2398 and 1024 positive COVID-19 cases were recorded in the selected areas, respectively, with an average monthly positivity rate of 40%. The number of clusters decreased from three clusters with an average of 11.3 positive cases per cluster in the pre-implementation period to no clusters in the post-implementation period. Implementation effectiveness showed compliance rates of 90% for barrier curtain placement and 100% for the social interaction protocol. Conclusion: This study confirms that physical barriers, specifically curtains, are effective measures against nosocomial COVID-19 transmission. It underscores the importance of adopting context-specific, cost-effective strategies, especially in low-to-middle-income countries, and provides a strong rationale for further research and implementation of such interventions.

Identification Of Locally Transmitted COVID-19 Spatial Clusters And Hotspots

Background: The coronavirus disease 2019 (COVID-19) is an emerging and rapidly evolving profound pandemic, which causes severe acute respiratory syndrome and results in significant case fatality around the world. We conducted this study to identify locally transmitted COVID-19 spatial clusters and hotspots in this phrase of the fourth wave in Vietnam. Data used and Methods: A total of 9,192 locally transmitted cases confirmed in this phrase in the fourth wave were used in study. Global and local Moran’s I and Getis-Ord’s G_i^* statistics were employed to identify spatial autocorrelation and hotspots of COVID-19 cases. Results: It was found that global Moran’s I statistic indicates a robust spatial autocorrelation of COVID-19 cases. Local Moran’s I statistic successfully identified three high-high spatial clusters of COVID-19 cases in Bac Giang (5,083 cases), Bac Ninh (1,407 cases), and Hanoi (464 cases). In addition, hotspots of COVID-19 cases were mainly detected in Bac Giang (5,083 cases), Bac Ninh (1,470 cases), Hanoi (464 cases), Hai Duong (51 cases), and Thai Nguyen (7 cases). Conclusion: The results of this work offer new perspectives on the geostatistical analysis of COVID-19 clusters and hotspots, which could help policy planners anticipate the dynamics of spatiotemporal transmission and develop critical control measures for SARS-CoV-2 in Vietnam. Future pandemics and epidemics can be avoided and controlled with the help of geospatial analysis techniques.

The utility of whole-genome sequencing to inform epidemiologic investigations of SARS-CoV-2 clusters in acute-care hospitals.

To evaluate the utility of selective reactive whole-genome sequencing (WGS) in aiding healthcare-associated cluster investigations. Mixed-methods quality-improvement study. Thes study was conducted across 8 acute-care facilities in an integrated health system. We analyzed healthcare-associated coronavirus disease 2019 (COVID-19) clusters between May 2020 and July 2022 for which facility infection prevention and control (IPC) teams selectively requested reactive WGS to aid the epidemiologic investigation. WGS was performed with real-time results provided to IPC teams, including genetic relatedness of sequenced isolates. We conducted structured interviews with IPC teams on the informativeness of WGS for transmission investigation and prevention. In total, 8 IPC teams requested WGS to aid the investigation of 17 COVID-19 clusters comprising 226 cases and 116 (51%) sequenced isolates. Of these, 16 (94%) clusters had at least 1 WGS-defined transmission event. IPC teams hypothesized transmission pathways in 14 (82%) of 17 clusters and used data visualizations to characterize these pathways in 11 clusters (65%). The teams reported that in 15 clusters (88%), WGS identified a transmission pathway; the WGS-defined pathway was not one that was predicted by epidemiologic investigation in 7 clusters (41%). WGS changed the understanding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission in 8 clusters (47%) and altered infection prevention interventions in 8 clusters (47%). Selectively utilizing reactive WGS helped identify cryptic SARS-CoV-2 transmission pathways and frequently changed the understanding and response to SARS-CoV-2 outbreaks. Until WGS is widely adopted, a selective reactive WGS approach may be highly impactful in response to healthcare-associated cluster investigations.

First documented gymnasium cluster of COVID-19 with whole genome sequencing in Australia.

Transmission of coronavirus disease 2019 (COVID-19) has been demonstrated in fitness settings internationally. We report the first documented case of transmission of COVID-19 in a gymnasium in Australia in 2020. Case finding and case interviews were conducted among attendees in a Western Sydney gymnasium, Australia. Whole genome sequencing using an amplicon-based approach was performed on all SARS CoV-2 polymerase chain reaction positive samples detected through surveillance. We show that five cases of COVID-19 were linked to the gymnasium, with transmission occurring on 7 July 2020, when the index case transmitted the infection to four other gymnasium attendees through the sharing of an enclosed space. There is an ongoing risk of transmission of COVID-19 within gymnasium environments and they are justifiably classified as a 'high-risk' venue. There may be a need to expand ventilation and space requirements to prevent transmission of COVID-19 in such settings in the context of severe COVID-19 variants or to prevent respiratory disease transmission in general.

Risk factors for transmission in a COVID-19 cluster infection in a high school in the Republic of Korea.

This study aimed to examine the scale, characteristics, risk factors, and modes of transmission in a coronavirus disease 2019 (COVID-19) outbreak at a high school in Seoul, Republic of Korea. An epidemiological survey was conducted of 1,118 confirmed cases and close contacts from a COVID-19 outbreak at an educational facility starting on May 31, 2021. In-depth interviews, online questionnaires, flow evaluations, and CCTV analyses were used to devise infection prevention measures. Behavioral and spatial risk factors were identified, and statistical significance was tested. Among 3rd-year students, there were 33 confirmed COVID-19 cases (9.6%). Students who used a study room in the annex building showed a statistically significant 4.3-fold elevation in their relative risk for infection compared to those who did not use the study room. Moreover, CCTV facial recognition analysis confirmed that 17.8% of 3rd-year students did not wear masks and had the lowest percentage of mask-wearers by grade. The air epidemiological survey conducted in the study room in the annex, which met the 3 criteria for a closed space, confirmed that there was only 10% natural ventilation due to the poor ventilation system. To prevent and manage the spread of COVID-19 in educational facilities, advance measures that consider the size, operation, and resources of each school are crucial. In addition, various survey methodologies should be used in future studies to quickly analyze a wider range of data that can inform an evidence-based quarantine response.

Discontinuation of admission screening for coronavirus disease 2019 (COVID-19) and the impact on in-hospital clusters of COVID-19: Experience at a tertiary-care center.

We evaluated the impact of discontinuing universal preadmission screening for severe acute respiratory coronavirus virus 2 (SARS-CoV-2) on the occurrence of nosocomial clusters of coronavirus disease 2019 (COVID-19) during the SARS-CoV-2 o (omicron) variant period. No increasing trend in nosocomial clusters was observed during community-based surges before and after discontinuation. This finding supports the safety of the practice change.

Genetic variants of SARS-CoV-2 circulated from Northern and Central Vietnam from January 2020 - April 2021

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causing novel coronavirus disease 2019 (COVID-19) appeared in Wuhan, Hubei province, China in late December 2019 and has rapidly spread worldwide. In this study, a total of 267 genomes of SARS CoV-2 viruses collected from 28 Center for Diseases Controls and hospitals in different provinces in Northern and Central Vietnam from January 2020 to April 2021 were sequenced and analyzed their diversity using the iSeq 100 platform. Results showed that most of the virus samples originated from domestic community patients (84.3%). Variable variants of SARS CoV-2 virus were detected within the three pandemic waves. The very first variant of SARS-CoV-2 in Viet Nam in January 2020 was 19B (Nextstrain Clade), 3/8 of the variants were from the international arrival samples group. In the first and second pandemic waves, lineage 20B was the most prevalent and this variant was found in Da Nang, Hai Duong and Thai Binh with a large number of patients. In the third wave of the COVID-19 pandemic, lineage 20I was the most dominant and detected in all provinces where the outbreak occurred. Five COVID-19 clusters caused by SARS-CoV-2 variant 20I were also found during this time.

SPATIAL CLUSTERING PHENOMENA OF COVID-19 CASES IN SELANGOR: A HOTSPOT ANALYSIS AND ORDINARY LEAST SQUARES METHOD

Abstract. An increase in number of Coronavirus disease 2019 (COVID-19) cases will lead to more cluster discovery in Malaysia. Furthermore, with the increasing population, city growth, workplace income needs, high-risk groups, and other relevant factors can contribute to the formation of the new clusters. The cluster distribution of the disease could be seen by mapping and spatial analysis to understand their spatial phenomena of the disease dynamics. The purpose of the study is to analyse the spatial distribution of COVID-19 cluster cases in Selangor for year 2020. Two objectives of the study are i) to determine the hotspot location of the COVID- 19 cluster, and ii)to examine the spatial distribution of the factors affecting the COVID-19 cluster. The data processing was conducted using hotspot analysis and ordinary least squares (OLS) in ArcGIS Pro and Microsoft Excel to explore the local disease phenomena. TheCOVID-19 cases was most prevalent in the Petaling district, followed by Hulu Langat and Klang. The virus had the least impact in Sabak Bernam, Hulu Selangor, Kuala Selangor, Sepang, Kuala Langat, and Gombak. Three environmental factors of population density, the effects of urbanisation, and workplace cases were influential variables at the local clusters. These findings could help the local agencies to facilitate and control the spread mode of the virus in a spatial human environment.

Identifying High-Risk Events for COVID-19 Transmission: Estimating the Risk of Clustering Using Nationwide Data.

The transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is known to be overdispersed, meaning that only a fraction of infected cases contributes to super-spreading. While cluster interventions are an effective measure for controlling pandemics due to the viruses' overdispersed nature, a quantitative assessment of the risk of clustering has yet to be sufficiently presented. Using systematically collected cluster surveillance data for coronavirus disease 2019 (COVID-19) from June 2020 to June 2021 in Japan, we estimated the activity-dependent risk of clustering in 23 establishment types. The analysis indicated that elderly care facilities, welfare facilities for people with disabilities, and hospitals had the highest risk of clustering, with 4.65 (95% confidence interval [CI]: 4.43-4.87), 2.99 (2.59-3.46), and 2.00 (1.88-2.12) cluster reports per million event users, respectively. Risks in educational settings were higher overall among older age groups, potentially being affected by activities with close and uncontrollable contact during extracurricular hours. In dining settings, drinking and singing increased the risk by 10- to 70-fold compared with regular eating settings. The comprehensive analysis of the COVID-19 cluster records provides an additional scientific basis for the design of customized interventions.

The Oral Cavity Potentially Serving as a Reservoir for SARS-CoV-2 but Not Necessarily Facilitating the Spread of COVID-19 in Dental Practice.

Intraoral tissues, secretions, and microenvironments may provide severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with the conditions necessary for viral cellular entry and inhabitation. The aim of the present study is to overview the oral cavity that potentially serves as a reservoir for SARS-CoV-2, and then discuss the possibility that such oral cavity facilitates the spread of coronavirus disease 2019 (COVID-19) in dental practice. Articles were retrieved from PubMed/Medline, LitCovid, ProQuest, Google Scholar, and preprint medRxiv databases. Results of the literature search indicated that SARS-CoV-2 host cell entry-relevant receptor and virus/cell membrane fusion mediators are expressed in major and minor salivary glands, tongue, taste bud, periodontal tissue, and dental pulp, which would be a target and reservoir for SARS-CoV-2. SARS-CoV-2 is present in saliva and gingival crevicular fluid of COVID-19 patients. These secretions would contaminate dental aerosol and droplet with SARS-CoV-2. SARS-CoV-2 inhabits periodontal pocket, gingival sulcus, and dental caries lesion, which could provide SARS-CoV-2 with a habitat. SARS-CoV-2 ribonucleic acid is preserved in dental calculus, which may inform of the previous infection with SARS-CoV-2. Despite involvement of the oral cavity in SARS-CoV-2 transmission and infection, to date, there have been no clusters of COVID-19 in dental practice. Dental settings are much less likely to facilitate the spread of COVID-19 compared with general medical settings, which may be explained by the situation of dentistry that the number of patients to visit dental offices/clinics was decreased during the COVID-19 pandemic, the characteristics of dentistry that dental professionals have maintained high awareness of viral infection prevention, adhered to a strict protocol for infection control, and been using personal protective equipment for a long time, the experimental results that dental devices generate only small amounts of aerosol responsible for the airborne viral transmission, irrigant from the dental unit contributes to the aerosol microbiota much rather than saliva, and the commonly used evacuation or suction system effectively reduces aerosol and droplet generation, and the possibility that human saliva exhibits the antiviral activity and the property to inhibit SARS-CoV-2 infection. It is considered that dental treatment and oral health care can be delivered safely in the COVID-19 era.

Ventilation improvement and evaluation of its effectiveness in a Japanese manufacturing factory

A coronavirus disease 2019 (COVID-19) cluster emerged in a manufacturing factory in early August 2021. In November 2021, we conducted a ventilation survey using the tracer gas method. Firstly, we reproduce the situation at the time of cluster emergence and examined whether the ventilation in the office was in a condition that increased the risk of aerosol transmission. Secondly, we verified the effectiveness of the factory’s own countermeasure implemented immediately after the August cluster outbreak. Furthermore, we verified the effectiveness of several additional improvement measures on the factory’s own countermeasures already installed in August. Under the conditions of the cluster emergence, the air changes per hour (ACH) value was 0.73 ACH on average. The ACH value was less than 2 ACH recommended by the Ministry of Health, Labour, and Welfare, suggesting an increased risk of aerosol transmission. The factory’s own countermeasures taken immediately in August were found to be effective, as the ACH value increased to 3.41 ACH on average. Moreover, it was confirmed that additional improvement measures on the factory’s own countermeasures increased the ACH value to 8.33 ACH on average. In order to prevent the re-emergence of COVID-19 clusters due to aerosol infection in the office, it was found that while continuing the factory’s own countermeasure, additional improvement measures should also be added depending on the number of workers in the room. In a company, it is important that workers themselves continue to take infection control measures autonomously, and confirming the effectiveness of the measures will help maintain workers’ motivation. We believe it is helpful that external researchers in multiple fields and internal personnel in charge of the health and safety department and occupational health work together to confirm the effectiveness of conducted measures, such as in this case.

COVID-19 transmission in dental practice during the pandemic: A questionnaire-based survey in private dental clinics in Japan

Background/purposeThe global coronavirus disease 2019 (COVID-19) pandemic continues to cause a significant impact on patient care due to its considerable transmissibility, morbidity, and mortality. The aim of this study was to investigate whether dental procedures performed at private dental clinics were associated with the occurrence of COVID-19 clusters and measures taken to prevent nosocomial infection of COVID-19.Materials and methodsAn online questionnaire-based survey on clinical activities, infection control measures, and confirmed or probable COVID-19 cases among patients and clinical staff during the pandemic (February 2020 to September 2021) was administered to dentists at private dental clinics in Nagano prefecture, Japan. Almost all dentists engaged in dental treatment were actively implementing standard precautions.ResultsTwenty-seven dental clinics provided dental care to infected patients (nine confirmed and eighteen probable), but there was no transmission from patients to staff. Ten clinics had staff who were infected, but none exhibited disease transmission from staff to patients.ConclusionThe results of this survey suggest that COVID-19 clusters might not occur in dental settings where appropriate protective measures are implemented.

Analysis of COVID-19 clusters involving vertical transmission in residential buildings in Hong Kong.

The Appendix is available in the online version of this article at 10.1007/s12273-022-0929-5.

Exploring spatiotemporal patterns of COVID-19 infection in Nagasaki Prefecture in Japan using prospective space-time scan statistics from April 2020 to April 2022

BackgroundUp to April 2022, there were six waves of infection of coronavirus disease 2019 (COVID-19) in Japan. As the outbreaks continue to grow, it is critical to detect COVID-19’s clusters to allocate health resources and improve decision-making substantially. This study aimed to identify active clusters of COVID-19 in Nagasaki Prefecture and form the spatiotemporal pattern of high-risk areas in different infection periods.MethodsWe used the prospective space-time scan statistic to detect emerging COVID-19 clusters and examine the relative risk in five consecutive periods from April 1, 2020 to April 7, 2022, in Nagasaki Prefecture.ResultsThe densely inhabited districts (DIDs) in Nagasaki City have remained the most affected areas since December 2020. Most of the confirmed cases in the early period of each wave had a history of travelling to other prefectures. Community-level transmissions are suggested by the quick expansion of spatial clusters from urban areas to rural areas and remote islands. Moreover, outbreaks in welfare facilities and schools may lead to an emerging cluster in Nagasaki Prefecture’s rural areas.ConclusionsThis study gives an overall analysis of the transmission dynamics of the COVID-19 pandemic in Nagasaki Prefecture, based on the number of machi-level daily cases. Furthermore, the findings in different waves can serve as references for subsequent pandemic prevention and control. This method helps the health authorities track and investigate outbreaks of COVID-19 that are specific to these environments, especially in rural areas where healthcare resources are scarce.

Clinical and epidemiological features of healthcare workers after a coronavirus disease 2019 cluster infection in Japan and the effects of Kampo formulas-Hochuekkito and Kakkonto: A retrospective cohort study.

It is expected that a low-toxicity natural compound like Kampo formulas would exhibit a preventive effect on COVID-19, in a global outbreak of coronavirus disease 2019 (COVID-19). Although the biological properties and safety of the representative Kampo, Hochuekkito (HET), and Kakkonto (KKT) have been confirmed in various animal model experiments and clinical studies, and in a few human studies to induce biological effects on various infectious diseases without significant toxicity, it is unclear whether HET and KKT are safe and effective for COVID-19 prevention. We summarized the clinical characteristics of HCWs and the preventive effects of HET and KKT. We performed a retrospective, single-center, cohort study that included 175 HCWs (aged 21-77 years) from a total number of 217 in a hospital with a history of COVID-19 cluster infection. In total, 175 HCWs were tested for severe acute respiratory coronavirus virus 2 (SARS-CoV-2) antibodies. We identified 27 patients (median age: 49 ± 10.7 years) who were diagnosed with COVID-19. The patients in the group that had a body mass index ≥ 25 had a high COVID-19 infection risk, while those in the group with a Kampo formula adherence rate ≥ 40% had a low COVID-19 risk. Patients in the group with an adherence rate ≥ 40%, as well as those in the current alcohol consumption group, were at a low risk of developing severe COVID-19. In conclusion, HET and KKT may have prevented the onset or worsening of COVID-19, which could be clinically used. Obesity might have increased the patients' susceptibility to COVID-19 and the disease severity.

Predictors of mortality in patients with COVID-19 infection in different health-care settings: A retrospective analysis from a CORACLE study group.

BackgroundDespite the large number of hospitalized patients affected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, few data are available about risk factors and mortality in subjects with nosocomially acquired respiratory infection of Coronavirus Disease 2019 (COVID-19).MethodsWe retrospectively evaluated in a multicentric study -during the pre-vaccination era-all patients admitted with confirmed diagnosis of nosocomial COVID-19 (NC). Patients were classified according to provenance: hospital-acquired NC or long-term care (LTC) facilities.ResultsAmong overall 1047 patients evaluated with COVID-19, 137 had a confirmed diagnosis of NC (13%). 78 (56.9%) patients had hospital-acquired NC and 59 (43%) had LTC NC. Overall mortality was 35.8%, in hospital-acquired NC 24.4%, in LTC NC 50.8% (p<0.001) (Log Rank test: p=0.001). Timing of diagnosis was significantly different between hospital acquired and LTC NC (3.5 vs 10 days, p<0.001). In multivariate analysis age, intensive-care unit admission, LTC provenance and sepsis were significant predictors of mortality in patients with NC infection.ConclusionPatients with NC are at higher risk of mortality (especially for LTC NC) and required preventive strategies, early diagnosis, and treatment to avoid COVID-19 cluster.

An analysis of the dynamic spatial spread of COVID-19 across South Korea

The first case of coronavirus disease 2019 (COVID-19) in South Korea was confirmed on January 20, 2020, approximately three weeks after the report of the first COVID-19 case in Wuhan, China. By September 15, 2021, the number of cases in South Korea had increased to 277,989. Thus, it is important to better understand geographical transmission and design effective local-level pandemic plans across the country over the long term. We conducted a spatiotemporal analysis of weekly COVID-19 cases in South Korea from February 1, 2020, to May 30, 2021, in each administrative region. For the spatial domain, we first covered the entire country and then focused on metropolitan areas, including Seoul, Gyeonggi-do, and Incheon. Moran’s I and spatial scan statistics were used for spatial analysis. The temporal variation and dynamics of COVID-19 cases were investigated with various statistical visualization methods. We found time-varying clusters of COVID-19 in South Korea using a range of statistical methods. In the early stage, the spatial hotspots were focused in Daegu and Gyeongsangbuk-do. Then, metropolitan areas were detected as hotspots in December 2020. In our study, we conducted a time-varying spatial analysis of COVID-19 across the entirety of South Korea over a long-term period and found a powerful approach to demonstrating the current dynamics of spatial clustering and understanding the dynamic effects of policies on COVID-19 across South Korea. Additionally, the proposed spatiotemporal methods are very useful for understanding the spatial dynamics of COVID-19 in South Korea.

Epidemiological Factors Associated with COVID-19 Clusters in Medical and Social Welfare Facilities.

The characteristics of coronavirus disease 2019 (COVID-19) clusters in medical and social welfare facilities and the factors associated with cluster size are still not yet fully understood. We reviewed COVID-19 cases in Japan identified from January 15 to April 30, 2020 and analyzed the factors associated with cluster size in medical and social welfare facilities. In this study, COVID-19 clusters were identified in 56 medical and 34 social welfare facilities. The number of cases in those facilities peaked after the peak of the general population. The duration of occurrence of new cases in clusters was positively correlated with the number of cases in both types of facilities (rho = 0.44, P < 0.001; and rho = 0.69, P < 0.001, respectively). However, the number of days between the first case in a prefecture and the onset of clusters was negatively correlated with the number of cases only in clusters in social welfare facilities (rho = - 0.4, P = 0.004). Our results suggest that COVID-19 cases in those facilities were prevalent in the latter phase of the disease's community transmission, although the underlying mechanisms for such a trend could differ between medical and social welfare facilities.