International Journal of Infectious Diseases

Since the first identified individual of 2019 novel coronavirus (COVID-19) infection on Jan 20, 2020 in South Korea, the number of confirmed cases rapidly increased. As of Feb 26, 2020, 1,261 cases of COVID-19 including 12 deaths were confirmed in South Korea. Using the incidence data of COVID-19, we estimate the reproduction number at 1.5 (95% CI: 1.4-1.6), which indicates sustained transmission and support the implementation of social distancing measures to rapidly control the outbreak.

Korean public health authorities raised the public alert to its highest level on February 23, 2020 to mitigate the 2019 novel coronavirus disease epidemic. We have identified that the mean delay from symptom onset to isolation was reduced to one day after raising the alert. Vigilance can reduce this interval.

We analyzed transmission of coronavirus disease 2019 in South Korea. We estimated that non-pharamaceutical measures reduced the immediate transmissibility by maximum of 34% for coronavirus disease 2019. Continuous efforts are needed for monitoring the transmissibility to optimize epidemic control.

ObjectivesElderly people had suffered disproportional burden of COVID-19. We hypothesized that males and females in different age groups might have different epidemic trajectories. MethodsUsing publicly available data from South Korea, daily new COVID-19 cases were fitted with generalized additive models, assuming Poisson and negative binomial distributions. Epidemic dynamics by age and gender groups were explored with interactions between smoothed time terms and age and gender. ResultsA negat...

On January 20, 2020, the first COVID-19 case was confirmed in South Korea. After a rapid outbreak, the number of incident cases has been consistently decreasing since early March; this decrease has been widely attributed to its intensive testing. We report here on the likely role of social distancing in reducing transmission in South Korea. Our analysis suggests that transmission may still be persisting in some regions.

Background: In Korea, a total of 10,840 confirmed cases of COVID-19 including 256 deaths have been recorded as of May 9, 2020. The time-delay adjusted case fatality risk (CFR) of COVID-19 in Korea is yet to be estimated. Methods: We obtained the daily series of confirmed cases and deaths in Korea reported prior to May 9, 2020. Using statistical methods, we estimated the time-delay adjusted risk for death from COVID-19 in Daegu, Gyeongsangbuk-do, other regions in Korea, as well as the entire coun...

BACKGROUNDThe clinical onset serial interval is often used as a proxy for the transmission serial interval of an infectious disease. For SARS-CoV-2/COVID-19, data on clinical onset serial intervals is limited, since symptom onset dates are not routinely recorded and do not exist in asymptomatic carriers. METHODSWe define the diagnostic serial interval as the time between the diagnosis dates of the infector and infectee. Based on the DS4C project data on SARS-CoV-2/COVID-19 in South Korea, we es...

We report the first 7,755 patients with confirmed COVID-19 in Korea as of March 13, 2020. A total of 66 deaths were identified, resulting case fatality proportion of 0.9%. Older people, and those with coexisting medical conditions were at risk for fatal outcomes. The highest number of cases were from Daegu, followed by Gyeongbuk, with elevated age-stratified case fatality. This summary may help to understand the disease dynamics in the early phase of COVID-19 outbreak, therefore, to guide future...

In early 2020, South Korea experienced a large coronavirus disease 2019 (COVID-19) outbreak. However, despite its proximity to China, where the virus had emerged, and the high population density of the Seoul metropolitan area, a major international hub, South Korea effectively contained the spread of COVID-19 using non-pharmaceutical interventions until vaccine distribution in 2021. Here, we built a metapopulation model with a susceptible-exposed-infectious-quarantined-recovered (SEIQR) structur...

ObjectivesThe distribution of the transmission onset of COVID-19 relative to the symptom onset is a key parameter for infection control. It is often not easy to study the transmission onset time, as is difficult to know who infected whom exactly when. MethodsWe inferred transmission onset time from 72 infector-infectee pairs in South Korea, either with known or inferred contact dates by means of incubation period. Combining this data with known information of infectors symptom onset, we could g...

BackgroundIn March 2020, overall, 37,000 international students from the country at risk of the 2019-novel coronavirus (COVID-19) infection will arrive in Seoul, South Korea. Individuals from the country at risk of COVID-19 infection have been included in a home-quarantine program, but the efficacy of the program is uncertain. MethodsTo estimate the possible number of infected individuals within the large influx of international students, we used a deterministic compartmental model for epidemic...

The novel coronavirus disease 2019 (COVID-19) outbreak in Republic of Korea has caused 3736 cases and 18 deaths by 1 March 2020. We modeled the transmission process in Republic of Korea with a stochastic model and estimated the basic reproduction number R0 as 2.6 (95%CI: 2.3-2.9) and 3.2 (95%CI: 2.9-3.5), under the assumption that the exponential growth starting 31 January and 5 February, 2020, respectively. Estimates of dispersion term (k) were larger than 10 significantly, which implies few su...

ObjectivesIn response to the World Health Organizations declaration of the COVID-19 pandemic in March 2020, nations worldwide, including Korea, implemented social distancing as a critical Non-Pharmaceutical Intervention (NPI) to curb the spread of the disease. Social distancing measures aimed to reduce person-to-person contact through various strategies such as facility restrictions, gathering limitations, travel bans, and lockdowns. MethodsThis study investigated the impact of social distancin...

In February and March 2020, COVID-19 epidemic in South Korea met a large black swan effect by a Sincheonji cult mass infection in Daegu-Gyeongbuk area. The black swan made it difficult to evaluate that the current policies for infection prevention including social distancing, closing schools, hand washing, and wearing masks good enough or not. Therefore, in this study, we evaluated basic reproduction number (R0) and time-dependent reproduction number (Rt) of confirmed cases based on various kind...

BackgroundBoth physicians and patients are proactive towards managing seasonal influenza in Japan and six drugs are approved. We aimed to clarify the status of anti-influenza drug use by analyzing real-world data. MethodsThis retrospective study analyzed open data from the National Database of Health Insurance Claims and Specific Health Checkups, which covers most claims data from national health insurance. We estimated the annual number of patients prescribed anti-influenza drugs, their age an...

ObjectiveIn late January 2020, the Japanese government carried out three evacuations by aircraft from Wuhan, China, to avoid further cases of coronavirus disease 2019 (COVID-19) among Wuhans Japanese residents. Evacuation by aircraft may be an effective countermeasure against outbreaks of infectious diseases, but evidence of its effect is scarce. This study estimated how many COVID-19 cases were prevented among the Japanese residents of Wuhan by the evacuation countermeasure. ResultsEleven impo...

BackgroundThe recent CoVID-19 pandemic has emerged as a threat to global health. Though current evidence on the epidemiology of the disease is emerging, very little is known about the predictors of recovery. ObjectivesTo describe the epidemiology of confirmed CoVID-19 patients in Republic of Korea and identify predictors of recovery. Materials and methodsUsing publicly available data for confirmed CoVID-19 cases from the Korea Centers for Disease Control and Prevention from January 20, 2020 to...

Between January 24 and March 10, of a total of 2,370 individuals who had contacted the first 30 cases of COVID-19, 13 were found to have COVID-19, resulting secondary attack rate of 0.55% (95% CI 0.31 - 0.96). Of 119 household contacts, 9 had infections resulting secondary attack rate of 7.56 (95% CI 3.73 - 14.26).

Following the first report of coronavirus disease 2019 (COVID-19) in Sapporo City, Hokkaido Prefecture, Japan on 14 February 2020, a surge of cases was observed in Hokkaido during February and March. As of 6 March, 90 cases were diagnosed in Hokkaido. Unfortunately, many infected persons may not have been recognized as cases due to having mild or no symptoms. We therefore estimated the actual number of COVID-19 cases in (i) Hokkaido Prefecture and (ii) Sapporo City using data on cases diagnosed ...

Current WHO reports claim a decline in COVID-19 testing. Many countries are reporting no new infections. In particular, USA, China and Japan have registered no cases and COVID-19 related deaths since May 15, 2023. To discuss consequences of ignoring SARS-CoV-2 infection, we compare endemic characteristics of the disease in 2023 with ones estimated before using 2022 datasets. The accumulated numbers of cases and deaths reported to WHO by 10 most infected countries and global figures were used to ...