Not so little differences: variation in hot weather risk to young children in New York City.

OBJECTIVES: High ambient temperatures are associated with significant health risk in the United States. The risk to children has been minimally explored, and often young children are considered as a single age group despite marked physiologic and social variation among this population from infancy through preschool. This study explored the heterogeneity of risk of heat among young children.

STUDY DESIGN: Using a time-stratified, case-crossover design, we evaluated associations between maximum daily temperature (Tmax) and ED visits (n = 1,002,951) to New York City (NYC) metropolitan area hospitals for children aged 0-4 years in May-September, 2005-2011.

METHODS: Conditional logistic regression analysis estimated risks for an interquartile range of Tmax for 0-6 lag days. Stratified analyses explored age strata by year, race/ethnic groups, and diagnostic codes. Sensitivity analyses controlled for same day ambient ozone, particulate matter <2.5 microns, and relative humidity and, separately, explored race groups without ethnicity and different diagnostic code groupings.

RESULTS: Children ages 0-4 years had increased risk of emergency department visits with increased Tmax on lag days 0, 1, and 3. The association was strongest on lag day 0, when an increase in Tmax of 13 °F conferred an excess risk of 2.6% (95% confidence interval [CI]: 2.2-3.0). Stratifying by age, we observed significant positive associations for same-day exposures, for 1-4 year olds. Children less than 1 year of age showed a significant positive association with Tmax only on lag day 3. The race/ethnicity stratified analysis revealed a similar lag pattern for all subgroups. The diagnostic group analysis showed percent excess risk for heat-specific diagnoses (16.6% [95% CI: 3.0-31.9]); general symptoms (10.1% [95% CI: 8.2-11.9]); infectious (4.9% [95% CI: 3.9-5.9]); and injury (5.1% [95% CI: 3.8-6.4]) diagnoses.

CONCLUSION: We found a significant risk of ED visits in young children with elevated Tmax. Risk patterns vary based on age with infants showing delayed risk and toddlers and preschoolers with same day risk. In addition, the finding of increased risk of injury associated with higher temperatures is novel. Altogether, these findings suggest a need for a tailored public health response, such as different messages to caregivers of different age children, to protect children from the effects of heat. Next steps include examining specific subcategories of diagnoses to develop protective strategies and better anticipate the needs of population health in future scenarios of climate change.