The association between tobacco or nicotine product use behaviors and non-compliance with mask wearing in COVID-19 pandemic period.

Objectives: It is necessary to investigate tobacco or nicotine product(TNP) use which acts as a risk factor for COVID-19 infection. Especially, mask wearing is difficult to practice when using TNP. Therefore, this study aimed to examine the association between TNP use behaviors and non-compliance with mask wearing in COVID-19 pandemic. Methods: The samples of 208,618 Korean adults aged 19 years or older were used. As an independent variable, TNP use behaviors such as TNP use status, changes in TNP use after COVID-19, TNP types, and attempt to quit were used. Logistic regression was performed on sex-stratified participants. Results: Among men, Odds ratio(OR) of current TNP users was 2.00(95%CI [1.66, 2.40]), and OR of former users was 1.32[1.09, 1.60] compared to never users. In women, OR was 1.50[1.00-2.26] for former users. Cigarette use was more associated with not wearing a mask than NCTNP use (OR=1.53[1.12, 2.08]). Men whose TNP use decreased had lower non-compliance (OR=0.52[0.36, 0.74]). Women whose TNP use increased had lower non-compliance (OR= 0.13[0.07, 0.26]). Conclusion: Current and former users were less likely to wear masks. Cigarette use was more associated with not wearing a mask than non-cigarette tobacco or nicotine products(NCTNP) use. Changes in TNP use showed association, but in opposite direction for men and women. Therefore, we suggest that more attention should be paid to TNP use prevention and cessation support during the epidemic of respiratory infectious diseases. In addition, it is necessary to identify risk factors of cigarette users in compliance with mask wearing.

Seroprevalence of severe acute respiratory syndrome coronavirus 2 antibodies during the third wave of coronavirus disease in the Seoul metropolitan area of Korea.

Objectives: After the third wave of coronavirus disease (COVID-19), by mid-February 2021, approximately 0.16% of the population was confirmed positive, which appeared to be one of the lowest rates worldwide at that time. However, asymptomatic transmission poses a challenge for COVID-19 surveillance. Therefore, a community-based serosurvey of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was conducted to understand the effectiveness of Korea's strong containment strategy. Methods: We collected 5,002 residual sera samples from January 30 to March 3, 2021 from 265 medical facilities in Seoul, 346 in Kyunggi-do' and 57 in Incheon. Among them, 60 samples from tertiary institutions were excluded. We defined the sub-regions according to the addresses of the medical facilities where the specimens were collected. Elecsys Anti-SARS-CoV-2 was used for the screening test, and positivity was confirmed using the SARS-CoV-2 sVNT Kit. Prevalence was estimated using sampling weight and the Wilson score interval for a binomial proportion with a 95% confidence interval. Results: Among the 4,942 specimens, 32 and 25 tested positive for COVID-19 in the screening and confirmatory tests, respectively. The overall crude prevalence of SARS-CoV-2 antibody was 0.51%. The population-adjusted overall prevalence was 0.55% in women and 0.38% in men. The region-specific estimation was 0.67% and 0.30% in Gyeonggi-do and Seoul, respectively. No positive cases were detected in Incheon. Conclusion: The proportion of undetected cases in South Korea remains low. Therefore, an infection control strategy with exhaustive tracing and widespread pre-emptive testing appears to be effective in containing the spread of the virus in the community.

The notable global heterogeneity in the distribution of COVID-19 cases and the association with pre-existing parasitic diseases.

BACKGROUND: The coronavirus Disease 2019 (COVID-19) is a respiratory disease that has caused extensive ravages worldwide since being declared a pandemic by the World Health Organization (WHO). Unlike initially predicted by WHO, the incidence and severity of COVID-19 appeared milder in many Low-to-Middle-Income Countries (LMIC). To explain this noticeable disparity between countries, many hypotheses, including socio-demographic and geographic factors, have been put forward. This study aimed to estimate the possible association of parasitic diseases with COVID-19 as either protective agents or potential risk factors. METHODS/PRINCIPAL FINDINGS: A country-level ecological study using publicly available data of countries was conducted. We conceptualized the true number of COVID-19 infections based on a function of test positivity rate (TPR) and employed linear regression analysis to assess the association between the outcome and parasitic diseases. We considered demographic, socioeconomic, and geographic confounders previously suggested. A notable heterogeneity was observed across WHO regions. The countries in Africa (AFRO) showed the lowest rates of COVID-19 incidence, and the countries in the Americas (AMRO) presented the highest. The multivariable model results were computed using 165 countries, excluding missing values. In the models analyzed, lower COVID-19 incidence rates were consistently observed in malaria-endemic countries, even accounting for potential confounding variables, Gross Domestic Product (GDP) per capita, the population aged 65 and above, and differences in the duration of COVID-19. However, the other parasitic diseases were not significantly associated with the spread of the pandemic. CONCLUSIONS/SIGNIFICANCE: This study suggests that malaria prevalence is an essential factor that explains variability in the observed incidence of COVID-19 cases at the national level. Potential associations of COVID-19 with schistosomiasis and soil-transmitted helminthiases (STHs) are worthy of further investigation but appeared unlikely, based on this analysis, to be critical factors of the variability in COVID-19 epidemic trends. The quality of publicly accessible data and its ecological design constrained our research, with fundamental disparities in monitoring and testing capabilities between countries. Research at the subnational or individual level should be conducted to explore hypotheses further.

Associations of symptom combinations with in-hospital mortality of coronavirus disease-2019 patients using South Korean National data.

BACKGROUND: There are various risk factors for death in coronavirus disease-2019 (COVID-19) patients. The effects of symptoms on death have been investigated, but symptoms were considered individually, rather than in combination, as predictors. We examined the effects of symptom combinations on in-hospital mortality. METHODS: Data from the Korea Disease Control and Prevention Agency were analyzed. A cohort of 5,153 patients confirmed with COVID-19 in South Korea was followed from hospitalization to death or discharge. An exploratory factor analysis was performed to identify symptom combinations, and the hazard ratios (HRs) of death were estimated using the Cox proportional hazard model. RESULTS: Three sets of symptom factors were isolated for symptom combination. Factor 1 symptoms were cold-like symptoms, factor 2 were neurological and gastrointestinal symptoms, and factor 3 were more severe symptoms such as dyspnea and altered state of consciousness. Factor 1 (HR 1.14, 95% confidence interval [95% CI] 1.01-1.30) and factor 3 (HR 1.25, 95% CI 1.19-1.31) were associated with a higher risk for death, and factor 2 with a lower risk (HR 0.71, 95% CI 0.71-0.96). CONCLUSIONS: The effect on in-hospital mortality differed according to symptom combination. The results are evidence of the effects of symptoms on COVID-19 mortality and may contribute to lowering the COVID-19 mortality rate. Further study is needed to identify the biological mechanisms underlying the effects of symptom combinations on mortality.

A measure to estimate the risk of imported COVID-19 cases and its application for evaluating travel-related control measures.

High connectivity between nations facilitates the spread of infectious diseases. We introduce an improved measure to estimate the risk of COVID-19 importation. The measure was applied to identify the effectiveness of travel-related control measures. We estimated the risk of importation, using the product of air-travel volume and COVID-19 prevalence in the area-of-origin. Travel volumes were acquired through real-time mobile data, and prevalence was calculated considering the time-varying strength of the COVID-19 testing policy. With the measure, the number of expected-imported cases was calculated, and compared with the reported-imported COVID-19 cases before and after post-entry quarantine for all entrants. The expected and reported-imported cases were well fitted (R2 = 0.8). A maximum of 35 undetected-imported cases was estimated to have entered Seoul, before the first imported COVID-19 case was confirmed. With the travel-related control measures, at most, 48 (73%) imported cases could be isolated from the local community. Our measure predicted trends in imported COVID-19 cases well. The method used to develop the measure can be applied to future emerging infectious diseases. Our results provide a 'real-world' evidence that travel-related control measures are effective at curbing further COVID-19 transmission.

The Unequal Effects of Social Distancing Policy on Subway Ridership during the COVID-19 Pandemic in Seoul, South Korea.

In the Republic of Korea, social distancing policies relied on voluntary participation by citizens and exhibited short-term changes. In this situation, the effects of such policies varied depending on each community's capacity to comply. Here, we collected subway ridership data for 294 stations on nine Seoul Metro lines and aggregated the data for each station to the 184 smallest administrative areas. We found that the mean percent change in subway ridership was fitted by an additive model of the log-transformed percent ratio of the restaurant industry (estimated degrees of freedom (EDF) = 3.24, P < 0.001), the Deprivation Index (DI) (EDF = 3.66, P = 0.015), and the proportion of essential workers (ß = - 0.10 (95% confidence interval - 0.15 to - 0.05, P < 0.001). We found a distinct decrease in subway ridership only in the least deprived areas, suggesting that social distancing is costly.

Generic Logic Model for Coronavirus Disease-2019 Responses Based on the South Korean Experience.

BACKGROUND: As the global coronavirus disease-2019 (COVID-19) pandemic continues, many countries have implemented public health policies, such as lockdowns and physical distancing measures, to prevent its spread. South Korea's response to COVID-19, which prevented an increase in confirmed cases and increased resilience, has been considered very effective. PURPOSE: To analyze Korea's response to COVID-19 in 2020 and develop a logic model to evaluate performance effectiveness in follow-up studies. METHODS: By content analysis of Korea Disease Control and Prevention Agency (KDCA) press releases, we defined the problems and identified the causes of the health and social effects of the COVID-19 outbreak. Next, we created a problem tree and developed a logic model that comprised inputs, activities, outputs, outcomes, and impacts. Finally, we held expert consultations to obtain expert opinions regarding the logic model and to ensure the model's validity. RESULTS: South Korea's COVID-19 response policy mitigated the social and health impacts. The 2020 COVID-19 responses had four outcomes (identifying cases on time, preventing transmission of coronavirus infection, effective treatment of COVID-19 cases, protecting public resilience and well-being) and 12 outputs; South Korea conducted 32 activities. CONCLUSION: The results can be a practical reference for managing problems faced in other countries. Korean policy may be of interest in the future for international decision-makers in charge of policy enforcement and those who may be called on to respond to new infectious diseases.

Interpretation of the Basic and Effective Reproduction Number.

In epidemiology, the basic reproduction number (R0) is a term that describes the expected number of infections generated by 1 case in a susceptible population. At the beginning of the coronavirus disease 2019 (COVID-19) pandemic, R0 was frequently referenced by the public health community and the wider public. However, this metric is often misused or misinterpreted. Moreover, the complexity of the process of estimating R0 has caused difficulties for a substantial number of researchers. In this article, in order to increase the accessibility of this concept, we address several misconceptions related to the threshold characteristics of R0 and the effective reproduction number (Rt). Moreover, the appropriate interpretation of the metrics is discussed. R0 should be considered as a population-averaged value that pools the contact structure according to a stochastic transmission process. Furthermore, it is necessary to understand the unavoidable time lag for Rt due to the incubation period of the disease.

Application of Testing-Tracing-Treatment Strategy in Response to the COVID-19 Outbreak in Seoul, Korea.

BACKGROUND: Following the coronavirus disease 2019 (COVID-19) outbreak in Wuhan, China, a total of 637 patients had been diagnosed with the disease in Seoul as of May 2, 2020. Our study aimed to describe the impact of the 3T strategies (preemptive testing, prompt tracing and proper treatment) on the epidemiological characteristics of COVID-19 in Seoul. METHODS: The descriptive and explanatory analysis was carried out on critical indicators such as epidemiological characteristics and key duration of patient status change from January 24 to May 2 in Seoul before and after preemptive testing for patients under investigation associated with COVID-19 clusters. RESULTS: Preemptive testing increased the positive test rate (3.9% to 4.2%), an asymptomatic case at diagnosis (16.9% to 30.6%), and reduced the time from symptom onset to quarantine (4.0 to 3.0 days). Prompt tracing decreased unknown sources of infection (6.9% to 2.8%), the mean number of contacts (32.2 to 23.6), and the time-varying reproduction number R(t) (1.3 to 0.6). With proper treatment, only 2 cases of mortality occurred, resulting in a fatality rate of just 0.3%. CONCLUSION: In the first wave of the COVID-19 pandemic lasting 100 days, the effect of the 3T strategies flattened the curve and decreased the time during which infected individuals were contagious, thereby lowering the R(t) below 1 in Seoul.

The Evolving Policy Debate on Border Closure in Korea.

OBJECTIVES: In this paper, we aimed to investigate the evolving debate over border closure in Korea during the coronavirus disease 2019 (COVID-19) pandemic, to address the main themes associated with border closure, and to discuss the factors that need to be considered when making such decisions. METHODS: We collated and reviewed previously conducted review studies on border closures during infectious disease outbreaks to derive relevant themes and factors. RESULTS: According to our systematic review on border closures and travel restrictions, the effects of such containment efforts are limited. We suggest considering the following factors when determining whether to impose border closure measures: (1) disease characteristics, (2) timeliness of implementation, (3) transmission delay and the basic reproduction number, (4) globalization and pandemics, and (5) social and economic costs. CONCLUSIONS: Our assessment indicates that the effects of border closures are at best temporary and limited. Alternative measures must be contemplated and implemented to suppress the spread of COVID-19 in particular and infectious diseases more broadly.

Estimating the Effectiveness of Non-Pharmaceutical Interventions on COVID-19 Control in Korea.

BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic has posed significant global public health challenges and created a substantial economic burden. Korea has experienced an extensive outbreak, which was linked to a religion-related super-spreading event. However, the implementation of various non-pharmaceutical interventions (NPIs), including social distancing, spring semester postponing, and extensive testing and contact tracing controlled the epidemic. Herein, we estimated the effectiveness of each NPI using a simulation model. METHODS: A compartment model with a susceptible-exposed-infectious-quarantined-hospitalized structure was employed. Using the Monte-Carlo-Markov-Chain algorithm with Gibbs' sampling method, we estimated the time-varying effective contact rate to calibrate the model with the reported daily new confirmed cases from February 12th to March 31st (7 weeks). Moreover, we conducted scenario analyses by adjusting the parameters to estimate the effectiveness of NPI. RESULTS: Relaxed social distancing among adults would have increased the number of cases 27.4-fold until the end of March. Spring semester non-postponement would have increased the number of cases 1.7-fold among individuals aged 0-19, while lower quarantine and detection rates would have increased the number of cases 1.4-fold. CONCLUSION: Among the three NPI measures, social distancing in adults showed the highest effectiveness. The substantial effect of social distancing should be considered when preparing for the 2nd wave of COVID-19.