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The aims of the study were to measure overall trends and to identify leading causes for pediatric emergency department (ED) visits among children aged 0 to 4 years.We conducted an 11-year population-based open cohort study using health administrative data from 2008 to 2018 in Ontario, Canada. All ED visits were extracted from the National Ambulatory Care Reporting System, along with the most responsible cause of each visit. Annual ED visit rates were calculated per 100 children in each year. Overall and disease-specific rates for all children were calculated and then stratified by sex and age groups. Relative percentage change in rates between 2008 and 2018 were calculated and compared using standardized differences (SDIFs). Statistical significance of time trends was tested using Poisson regression.This study included an average of 911,566 children from 2008 to 2018. All-cause ED visit rates increased by 28.2% from 2008 to 2018 (43.24-55.42 per 100, SDIF0.1). Respiratory diseases were consistently the top cause of ED visits, and contributed to 1 in 3 ED visits in 2018. These respiratory conditions include asthma, asthma-related diseases (bronchiolitis, bronchitis, influenza, and pneumonia), and other respiratory diseases. Respiratory ED visit rates increased by 32.8% from 2008 to 2018 (11.51-15.28 per 100, SDIF0.1), driven by a 46.4% (14.58-21.35 per 100, SDIF0.1) increase among children younger than 1 year. There was a 78.0% increase in ED visits for bronchiolitis in infants (1.45-2.58 per 100, SDIF0.1).Respiratory diseases like bronchiolitis among infants were the consistent leading cause for ED visits. All-cause ED visit rates among young children increased by 28.17% from 2008 to 2018.

Owing to their greater outdoor activity and ongoing lung development, children are particularly vulnerable to the harmful effects of exposure to fine particulate matter (PM2.5). However, the effects of PM2.5 components are poorly understood. This study aimed to use a longitudinal birth cohort of children with physician-diagnosed incident asthma to investigate the effect of PM2.5 components at birth on morbidity measured by health services utilization. Of 1277 Toronto Child Health Evaluation Questionnaire (T-CHEQ) participants, the study population included 362 children diagnosed with asthma who were followed for a mean of 13 years from birth until March 31, 2016, or loss-to-follow-up. Concentrations of PM2.5 and its components were assigned based on participants’ postal codes at birth. Study outcomes included counts of asthma, asthma-related, and all-cause health services use. Poisson regression in single-, two-, and multi-pollutant models was used to estimate rate ratios (RR) per interquartile range (IQR) increase of exposures. Covariates were included in all models to further adjust for potential confounding. The adjusted RR for sulfate (SO4) and all-cause hospitalizations was statistically significant with RR = 2.23 (95% confidence interval [CI]: 1.25–3.96) in a multi-pollutant model with nitrogen dioxide (NO2) and ozone (O3). In multi-pollutant models with oxidants, the adjusted RRs for SO4 of all-cause hospitalizations and emergency department (ED) visits were also statistically significant with RR = 2.31 (95% CI: 1.32–4.03) and RR = 1.39 (95% CI: 1.02–1.90), respectively. While unadjusted single-pollutant RRs for asthma-specific and asthma-related health services use with the SO4 component of PM2.5 were above one, none were statistically significant. This study found significant associations with exposure to SO4 in PM2.5 and all-cause acute care, chiefly for hospitalizations, in children with asthma.

Background Quantifying the impact of environmental factors on COVID-19 transmission is crucial in preventing more cases. Ultraviolet (UV) radiation and ozone (O3) have reported antimicrobial properties but few studies have examined associations with community infectivity of COVID-19. Research suggests UV light can be preventative while the effect of O3 is contested. We sought to determine the relationship between UV, O3, and COVID-19 incidence in Ontario, Canada. Methods In our time series analyses, we calculated daily incidence rates and reproductive number (Rt) from 34,975 cases between January and June 2020 across 34 Ontario Public Health Units. We used generalised linear models, adjusting for potential confounders, to calculate point estimates (PE) and 95% confidence intervals (CI) for UV and O3. Analyses were further stratified by age groups and outbreaks at institutions versus community. Results We found that 1-week averaged UV was significantly associated with a 13% decrease (95% CI: 0.80–0.96) in overall COVID-19 Rt, per unit increase. A negative association with UV was also significant among community outbreaks (PE: 0.88, 95% CI: 0.81–0.96) but not institutional outbreaks (PE: 0.94, 95% CI: 0.85–1.03). A positive association of O3 with COVID-19 incidence is strongly suggested among institutional outbreak cases (PE: 1.06, 95% CI: 1.00–1.13). Conclusion Our study found evidence to support the hypothesis that higher UV reduced transmission of COVID-19 and some evidence that ground-level O3 positively influenced COVID-19 transmission. Setting of infection should be strongly considered as a factor in future research. UV and O3 may explain some of COVID-19's seasonal behaviour., Highlights • Studied effects of UV and ozone on COVID-19 in Ontario, Canada. • Quantified transmission from 35,000 Ontario COVID-19 cases from January to June 2020. • Higher 1-week lagged UV was associated with decreased COVID-19 transmission. • Higher 1-week lagged O3 was associated with increased COVID-19 transmission. • O3 was a factor for institutional outbreaks while UV was for community outbreaks.

Background: Parents often question why one of their children have asthma while their siblings do not. With twins, this is especially perplexing. The gene-environment interaction hypothesis suggests that early-life environmental exposures interact with genes, leading to asthma and atopic diseases. This study aims to investigate potential risk factors that modifies the risk of asthma and other atopic diseases between twins in shared early-life environments. Methods: A paired population-based open cohort study was conducted using health administrative data between April 1, 2004 and March 31, 2019 from Ontario, Canada. The study population consisted of Ontario twins born between 2004-2017. Multivariable logistic regression was used to estimate adjusted odds ratios (aOR) and 95% confidence intervals (CI) for associations between discordance (asthma, allergic rhinitis, and eczema) and early-life factors. Results: This study included 24,392 twin-pairs from Ontario Canada aged 1 to 15 years. 15·7%, 17·9%, and 31·9% of twin-pairs had discordant asthma, allergic rhinitis, and eczema respectively. Compared to female-female twin-pairs, male-female and male-male twin-pairs were 69% (95% CI: 1·54-1·84) and 35% (95% CI: 1·23-1·49) higher odds to have asthma discordance, respectively. Twins who were delivered by Caesarian-section had significantly higher odds of asthma (aOR: 1·09, 95% CI: 1·01-1·18) and allergic rhinitis (aOR: 1·11, 95% CI: 1·04-1·20), and is strongly suggested for eczema discordance (aOR: 1·05, 95% CI: 1·00-1·12), compared to pairs who had vaginal births. Conclusion: This population-based study found associations of various early-life factors and asthma and allergic diseases discordance between twins. While early-life factors were associated with disease risks in children, genetic factors played a strong underlying role. Funding: This study was funded by the Asthma and COPD Program, Ontario Ministry of Health and Long-Term Care (MOHLTC). Declaration of Interest: None to declare. Ethical Approval: Ethics approval for this study was obtained from the Hospital for Sick Children Research Ethics Board in Toronto, Ontario.

The SARS-CoV-2 is a novel coronavirus identified as the cause of COVID-19, and as the pandemic evolves, many have made parallels to previous epidemics such as SARS-CoV (the cause of an outbreak of severe acute respiratory syndrome [SARS]) in 2003. Many have speculated that, like SARS, the activity of SARS-CoV-2 will subside when the climate becomes warmer. We sought to determine the relationship between ambient temperature and COVID-19 incidence in Canada. We analyzed over 77,700 COVID-19 cases from four Canadian provinces (Alberta, British Columbia, Ontario, and Quebec) from January to May 2020. After adjusting for precipitation, wind gust speed, and province in multiple linear regression models, we found a positive, but not statistically significant, association between cumulative incidence and ambient temperature (14.2 per 100,000 people; 95%CI: −0.60–29.0). We also did not find a statistically significant association between total cases or effective reproductive number of COVID-19 and ambient temperature. Our findings do not support the hypothesis that higher temperatures will reduce transmission of COVID-19 and warns the public not to lose vigilance, and to continue practicing safety measures such as hand washing, social distancing, and use of facial masks despite the warming climates., Graphical abstract Unlabelled Image, Highlights • Studied effects of temperature on COVID-19 with daily meteorological data in Canada • Used 99.6% of Canada's cases from January to May 2020 (77,700+) from four provinces • No significant association between ambient temperature and COVID-19 incidence