Variability of heat stress illness (HSI) by urbanicity and climate region has rarely been considered in previous HSI studies. We investigated temporal and geographic trends in HSI emergency department (ED) visits in CDC Environmental Public Health Tracking Network (Tracking) states for 2005-2010. We obtained county-level HSI ED visit data for 14 Tracking states. We used the National Center for Health Statistics Urban-Rural Classification Scheme to categorize counties by urbanicity as (1) large central metropolitan (LCM), (2) large fringe metropolitan, (3) small-medium metropolitan, or (4) nonmetropolitan (NM). We also assigned counties to one of six US climate regions. Negative binomial regression was used to examine trends in HSI ED visits over time across all counties and by urbanicity for each climate region, adjusting for pertinent variables. During 2005-2010, there were 98,462 HSI ED visits in the 14 states. ED visits for HSI decreased 3.0% (p < 0.01) per year. Age-adjusted incidence rates of HSI ED visits increased from most urban to most rural. Overall, ED visits were significantly higher for NM areas (IRR = 1.41, p < 0.01) than for LCM areas. The same pattern was observed in all six climate regions; compared with LCM, NM areas had from 14 to 90% more ED visits for HSI. These findings of significantly increased HSI ED visit rates in more rural settings suggest a need to consider HSI ED visit variability by county urbanicity and climate region when designing and implementing local HSI preventive measures and interventions.
Keywords: Emergency department; Heat illness; Metropolitan; Nonmetropolitan; Time trend; Urbanization.