Background: This study aimed to identify the incidence rate of episodes diagnosed with influenza and the effects of age-period-cohort (APC) in Koreans. Methods: The 2009–2018 National Health Insurance Research Database was used for analysis. All time-related claims connected relatively short window period in 100 days. The case definition was defined by all codes diagnosed with J09, J10, and J11. Calculation of the incidence rate and APC analysis adjusted income levels by insurance type, metropolitan city was performed to identify the characteristics of episodes diagnosed with influenza. Results: Incidence rate by age and cohort gradually increased since 2014. The incidence rate of males aged 0–4 years was 171.02 and that of females was 173.31 in 2015–2016 season. In males, 29.19 in 1963 cohort and 243.79 in 2013 cohort were confirmed as high incidence rates in 2017–2018 season. In the females, a high incidence was confirmed in 1953–1967 cohort and 1978–1987 cohort, and the incidence was 251.38 in 2013–2017 cohort. APC effects showed a high relative risk in the infants, the pandemic influenza season in 2010 (1/7/2009 to 30/6/2010) and the adults of 1978–1987 cohort. Conclusion Since 2014, influenza outbreaks have been increasing every year. The start year of free vaccination decreased the incidence in infants and adults over 65 years of age but the incidence increased from the following year. Because influenza can be primarily prevented by vaccination, reinforcement of vaccination in infants may reduce the disease burden in their parents, and also the risk of infection caused by family transmission. A new vaccination strategy is needed to reduce the incidence and burden of diseases caused by influenza infection.

Background: Mortality of coronavirus disease 2019 (COVID-19) is a major concern for quarantine departments in all countries. This is because the mortality of infectious diseases determines the basic policy stance of measures to prevent infectious diseases. Early screening of high-risk groups and taking action are the basics of disease management. This study examined the correlation of comorbidities on the mortality of patients with COVID-19. Methods: We constructed epidemiologic characteristics and medical history database based on the Korean National Health Insurance Service Big Data and linked COVID-19 registry data of Korea Centers for Disease Control & Prevention (KCDC) for this emergent observational cohort study. A total of 9,148 patients with confirmed COVID-19 were included. Mortalities by sex, age, district, income level and all range of comorbidities classified by International Classification of Diseases-10 based 298 categories were estimated. Results: There were 3,556 male confirmed cases, 67 deaths, and crude death rate (CDR) of 1.88%. There were 5,592 females, 63 deaths, and CDR of 1.13%. The most confirmed cases were 1,352 patients between the ages of 20 to 24, followed by 25 to 29. As a result of multivariate logistic regression analysis that adjusted epidemiologic factors to view the risk of death, the odds ratio of death would be hemorrhagic conditions and other diseases of blood and blood-forming organs 3.88-fold (95% confidence interval [CI], 1.52–9.88), heart failure 3.17-fold (95% CI, 1.88–5.34), renal failure 3.07-fold (95% CI, 1.43–6.61), prostate malignant neoplasm 2.88-fold (95% CI, 1.01–8.22), acute myocardial infarction 2.38-fold (95% CI, 1.03–5.49), diabetes was 1.82-fold (95% CI, 1.25–2.67), and other ischemic heart disease 1.71-fold (95% CI, 1.09–2.66). Conclusion We hope that this study could provide information on high risk groups for preemptive interventions. In the future, if a vaccine for COVID-19 is developed, it is expected that this study will be the basic data for recommending immunization by selecting those with chronic disease that had high risk of death, as recommended target diseases for vaccination.

Background: This study aimed to investigate the effect of antiviral therapy following influenza outpatient episodes on the incidence of hospitalized pneumonia episodes, one of secondary complications of influenza. Methods: In the National Health Insurance Research Database, data from July 2013 to June 2018 were used. All of the claim data with diagnoses of influenza and pneumonia were converted to episodes of care after applying 100 days of window period. With the 100-day episodes of care, the characteristics of influenza outpatient episodes and antiviral therapy for influenza, the incidence of hospitalized pneumonia episodes following influenza, and the effect of antiviral therapy for influenza on hospitalized pneumonia episodes were investigated. Results: The crude incidence rate of hospitalized pneumonia after influenza infection was 0.57% in both males and females. Factors affecting hospitalized pneumonia included age, income level except self-employed highest (only in females), municipality, medical institution type, precedent chronic diseases except hepatitis (only in females) and antiviral therapy. In the 2017 flu season, the relative risk was 0.38 (95% confidence interval [CI], 0.29–0.50) in males aged 0–9 and 0.43 (95% CI, 0.32–0.57) in females aged 0–9 without chronic diseases, and it was 0.51 (95% CI, 0.42–0.61) in males aged 0–9 and 0.42 (95% CI, 0.35–0.50) in females aged 0–9 with one or more chronic diseases in the aspect of the effect of antiviral therapy on pneumonia. It suggests that antiviral therapy may decrease the incidence of pneumonia after influenza infection. Conclusion After outpatient episode incidence of influenza, antiviral treatment has been shown to reduce the incidence of hospitalized pneumonia, especially in infants and children, during pandemic season 2017. Antiviral therapy for influenza is recommended to minimize burden caused by influenza virus infection and to reduce pneumonia. In addition, medical costs of hospitalization may decrease by antiviral therapy, especially in infants and children.

Objective: It is difficult to predict the treatment response of tissue after stereotactic radiosurgery (SRS) because radiation necrosis (RN) and tumor recurrence can coexist. Our study aimed to predict tumor recurrence, including the recurrence site, after SRS of brain metastasis by performing a longitudinal tumor habitat analysis. Materials and Methods: Two consecutive multiparametric MRI examinations were performed for 83 adults (mean age, 59.0 years; range, 27–82 years; 44 male and 39 female) with 103 SRS-treated brain metastases. Tumor habitats based on contrastenhanced T1- and T2-weighted images (structural habitats) and those based on the apparent diffusion coefficient (ADC) and cerebral blood volume (CBV) images (physiological habitats) were defined using k-means voxel-wise clustering. The reference standard was based on the pathology or Response Assessment in Neuro-Oncologycriteria for brain metastases (RANO-BM). The association between parameters of single-time or longitudinal tumor habitat and the time to recurrence and the site of recurrence were evaluated using the Cox proportional hazards regression analysis and Dice similarity coefficient, respectively. Results: The mean interval between the two MRI examinations was 99 days. The longitudinal analysis showed that an increase in the hypovascular cellular habitat (low ADC and low CBV) was associated with the risk of recurrence (hazard ratio [HR], 2.68; 95% confidence interval [CI], 1.46–4.91; P = 0.001). During the single-time analysis, a solid low-enhancing habitat (low T2 and low contrast-enhanced T1 signal) was associated with the risk of recurrence (HR, 1.54; 95% CI, 1.01–2.35; P= 0.045). A hypovascular cellular habitat was indicative of the future recurrence site (Dice similarity coefficient = 0.423). Conclusion After SRS of brain metastases, an increased hypovascular cellular habitat observed using a longitudinal MRI analysis was associated with the risk of recurrence (i.e., treatment resistance) and was indicative of recurrence site. A tumor habitat analysis may help guide future treatments for patients with brain metastases.