Objectives There is a great deal of interest in the possibility that environmental factors may influence the risk of developing allergic rhinitis (AR) in early life. We investigated the simultaneous effects of mode of delivery and duration of breastfeeding on the development of AR in children. Methods Data from 1,374 children participating in the Allergic Rhinitis Cohort Study for kids (ARCO-kids study) was analyzed. All subjects were divided into AR or non-allergic rhinitis (NAR) groups. Data on environmental factors, mode of delivery and duration of breastfeeding were collected using a questionnaire. Results Compared with short-term breastfeeding (<6 months), long-term breastfeeding (≥12 months) was significantly associated with a lower prevalence of AR (adjusted odds ratio [aOR], 0.54; 95% confidence interval [CI], 0.34 to 0.88). Children in the AR group also had a higher cesarean delivery rate than those in the NAR group (39.1% vs. 32.8%, P =0.05). Regarding the combined effects of mode of delivery and duration of breastfeeding, long-term breastfeeding with a vaginal delivery strongly suppressed the development of AR, compared to short-term breastfeeding with a cesarean delivery (aOR, 0.47; 95% CI, 0.30 to 0.73). Conclusion Long-term breastfeeding (≥12 months) and a vaginal delivery are associated with a lower risk of developing childhood AR.

Background Complete contact tracing of COVID-19 patients in Korea allows a unique opportunity to investigate cluster characteristics. This study aimed to investigate all the reported COVID-19 clusters in Seoul Metropolitan area from January 23 to September 24, 2020. Methods Publicly available COVID-19 data was collected from the Seoul Metropolitan city and Gyeonggi Province. Community clusters with ≥ 5 cases were characterized by size and duration and then categorized using K-means clustering, and the correlation between the types of clusters and the level of social distancing was investigated. Results A total of 134 clusters including 4,033 cases were identified. The clusters were categorized into small (Type I, II), medium (type III), and large (type IV) clusters. With the same number of daily confirmed cases, cases were composed of different types of clusters by different periods of time. Raising social distancing was related with shifting types of clusters from large to small sized clusters. Conclusions Classification of clusters may provide opportunities to better portray the pattern of COVID-19 outbreaks and implement more effective strategies. Social distancing administered by the government may be effective in suppressing large clusters but may not be effective in controlling small and sporadic clusters.

The aim of this study was to examine the association between indoor tanning use and the risk of overall and early-onset (age < 50) melanoma and non-melanoma skin cancer (NMSC). To evaluate the association between indoor tanning and skin cancer, a systematic review of the literature published until July 2021 was performed using PubMed, EMBASE, and MEDLINE. Summary relative risk (RR) from 18 studies with 10,406 NMSC cases and 36 studies with 14,583 melanoma cases showed significant association between skin cancer and indoor tanning (melanoma, RR= 1.27, 95% CI 1.16–1.39; NMSC, RR = 1.40, 95% CI 1.18–1.65; squamous cell carcinoma (SCC), RR = 1.58, 95% CI 1.38–1.81; basal cell carcinoma (BCC), RR = 1.24, 95% CI 1.00–1.55). The risk was more pronounced in early-onset skin cancer (melanoma, RR = 1.75, 95% CI 1.14–2.69; NMSC, RR = 1.99, 95% CI 1.48–2.68; SCC, RR = 1.81, 95% CI 1.38–2.37; BCC, RR = 1.75, 95% CI 1.15–2.77). Moreover, first exposure at an early age (age ≤ 20 years) and higher exposure (annual frequency ≥ 10 times) to indoor tanning showed increasing risk for melanoma (RR = 1.47, 95% CI 1.16–1.85; RR = 1.52, 1.22–1.89) and NMSC (RR = 2.02, 95% CI 1.44–2.83; RR = 1.56, 95% CI 1.31–1.86). These findings provide evidence supporting primary prevention policies regulating modifiable behaviors to reduce the additional risk of skin cancer among younger adults.

An increased risk of gastric cancer for pickled vegetable and salted fish intake has been suggested, yet the lack of a dose-response association warrants a quantitative analysis. We conducted a meta-analysis, combining results from our analysis of two large Korean cohort studies and those from previous prospective cohort studies. We investigated the association of pickled vegetable and salted fish intake with gastric cancer in the Korean Genome Epidemiology Study and the Korean Multi-center Cancer Cohort Study using Cox proportional hazard models. We then searched for observational studies published until November 2019 and conducted both dose-response and categorical meta-analyses. The pooled relative risk (RR) of gastric cancer incidence was 1.15 (95% Confidence Interval (CI), 1.07–1.23) for 40 g/day increment in pickled vegetable intake in a dose-response manner (P for nonlinearity = 0.11). As for salted fish intake, the pooled risk of gastric cancer incidence was 1.17 (95% CI, 0.99–1.38) times higher, comparing the highest to the lowest intake. Our findings supported the evidence that high intake of pickled vegetable and salted fish is associated with elevated risk of gastric cancer incidence.

Objectives: During the coronavirus disease (COVID-19) pandemic, crude incidence and mortality rates have been widely reported; however, age-standardized rates are more suitable for comparison. In this study, we estimated and compared the age-standardized incidence, mortality, and case fatality rates among countries and investigated the relationship between these rates and factors associated with healthcare resources: gross domestic product per capita, number of hospital beds per population, and number of doctors per population. Methods:The incidence, mortality, and case fatality rates of 79 countries were age-standardized using the WHO standard population. The rates for persons 60 years or older were also calculated. The relationships among the rates were analysed using trend lines and coefficients of determination (R 2 ). The Pearson's correlation coefficients between the rates and the healthcare resource-related factors were calculated. Results:The countries with the highest age-standardized incidence, mortality, and case fatality rates were Czechia (14,253 cases/100,000), Mexico (182 deaths/100,000), and Mexico (6.7%), respectively. The R 2 between the incidence and mortality rates was 0.8520 for all ages and 0.9452 for those 60 years or older. The healthcare resources-related factors were associated positively with incidence rates, and negatively with case fatality rates: the correlations were weaker among the elderly.Conclusions: Compared to age-standardized rates, crude rates showed greater variation between countries. Medical resources may be important in preventing COVID-19-related deaths; however, considering the small variation in fatality among the elderly, prevention such as vaccination is more important especially for the elderly population to minimize the mortality rates in the elderly population.