Given the background of climate change, there is an increasing demand for public health to characterize weather-related illness. The public health impact of extreme heat or cold events can be characterized from Emergency Department syndromic surveillance data to monitor conditions which aren’t routinely captured by other surveillance methods. However case detection is limited to the selected terminology in the syndrome definition. A statistical approach to monitor all-cause, excess morbidity during a weather event and estimate the risk attributed to specific conditions would allow public health to 1) characterize the broad impact of these events more appropriately and 2) create targeted intervention to reduce overall burden in at risk populations due to specific causes. The Chicago heat wave in 1995 captured a lot of attention over the estimates of the magnitude of heat-related deaths and the debate over conservative verses broad case definitions. Shen compared deaths coded from a broadly-defined, heat-related mortality definition from the Cook County Medical Examiner’s Office during the heat wave against excess all-cause mortality and found that even a broadly- defined heat-related classifier underestimated deaths due to the heat wave (19 per 100,000 vs. 24-25 per 100,000). Our emergency preparedness staff has questioned the completeness of heat-related estimates from ED data. Fewer studies have reviewed non-fatal heat-related illness. Re-visiting the heat wave of 1995, Semenza analyzed hospital discharge data to characterize the underlying diseases of at risk populations. The majority of excess hospitalizations were the result of dehydration, heat stroke, heat exhaustion and acute renal failure in the primary diagnosis. Co-morbid conditions were exacerbated by cardiovascular disease, diabetes, renal disease and nervous system disorders, particularly in the population 65 and older. A study by Knowlton looked specifically at emergency department visits during the 2006 California heat wave and found a significant increase in ED visits but not hospitalizations. Stratifying by region, age (under 5, 5-64 and 65 and older), conditions, race and ethnicity they calculated risk ratios in a case-crossover design, from a baseline established from the weeks surrounding the heat wave. There were significant increases for acute renal failure, cardiovascular disease, diabetes, electrolyte imbalance and nephritis. Patterns that were distinct for ED visits included electrolyte imbalance in the youngest age group, and cardiac-related illness in Hispanic population. There have been very limited studies into excess visits due to violence or mental health conditions in syndromic data during a heat wave. These are important health issues, particularly in our urban centers that warrant further investigation.
Syndrome definitions sometime exclude common terms, such as dehydration, over concerns that the baseline presents less specificity to characterize heat related illness. However, a conservative definition underestimates the true impact of a critical public health event, such as a heat wave, which limits our ability to assess the magnitude and appropriate prevention and response.