Heat-Related Illness

• The numbers and rates of hospitalizations, emergency department (ED) visits, or deaths directly attributed to heat-related illness by year, gender, or age group in Minnesota.

• If a segment of a population is at higher risk for hospitalization, a visit to the ED, or death resulting from heat in Minnesota.

• Allow for a better understanding of spatial and temporal trends of extreme heat.

• Average heat index by county in Minnesota.

• Number of days of extreme heat in each county in Minnesota.

• How heat index relates to heat-illness by year and month.

• Provide information to the public about heat-related illness hospitalizations, ED visits, and deaths in Minnesota.

• State and local partners can use these data for program planning and evaluation.

• The general public can use this information to better understand temperature distribution in Minnesota and their area’s risk of extreme heat.

• These hot weather data and maps can be used to:

• Inform which Minnesota counties should be targeted for outreach and prevention efforts.

• Educate the public about the health effects from extreme temperature.

• The total burden of heat-related illness in a population.

• The number of people hospitalized or who visited the ED for heat-related illness. Because personal identifiers are removed from the hospital discharge data before analysis, we cannot identify individuals who may receive care at more than one facility.

• Heat-related illness can manifest in numerous and unobvious ways, for this reason heat may not be listed as the primary diagnosis. This analysis only captures cases where heat-related illness is explicitly listed and thus does not capture the full extent of heat-related illness, since they are sometimes not coded as heat-related.

• Deaths attributed to heat are very rare because often heat-related illness may not be listed as the underlying cause of death. This analysis only includes deaths where heat-related illness is explicitly recorded as an underlying or contributing cause of death and does not capture the full extent of heat-related deaths.

Hospitalizations/ED visits:

• Minnesota residents who are hospitalized or visit the emergency department in the warm weather months (May-September) with a diagnosis of directly attributable heat-related illness, defined as having any of the following ICD-9-CM codes: 992.0-992.9, E900.0, and E900.9 and ICD-10-CM codes: T67, X30, or X32 (excluding cases with a code W92).

• The data source for hospitalizations and ED visits is the Minnesota Hospital Discharge Data. The Minnesota Hospital Discharge Data collects hospital discharge information from acute care hospitals submitting data to the Minnesota Hospital Association (MHA). MN EPHT receives Minnesota Hospital Discharge Data from the Injury and Violence Prevention Unit at MDH.

• Hospitalizations include out-of-state hospitalizations of Minnesota residents in the nearby states of North Dakota, South Dakota, and Iowa. ED visits only include out -of-state hospitalizations of Minnesota residents after the year 2005.

Deaths:

• Minnesota residents deceased during the warm weather months (May-September) with ICD-10 code T67(heat-related illness) listed as a contributing cause of death on the death certificate record or accompanied by ICD-10 code X30 as a contributing cause of death.

• The data source for deaths is the Minnesota Mortality Data, which contains information on demographic and cause of death data collected from death certificates. Minnesota Mortality Data is maintained by the Center for Health Statistics at MDH. MN EPHT receives Minnesota Mortality data from the Injury and Violence Prevention Unit at MDH.

• The average summer heat index from 2019-2022 was determined by averaging the maximum daily heat index from May through September for the three years for each county. Three years of data were used to determine the average heat index because temperatures can vary considerably every year. Looking at multiple years helps to provide a better understanding of typical temperatures.

• For this analysis, extreme heat days were defined as days that had a heat index over the 95th percentile of the baseline (based on the daily heat index for the years 1991-2020).

• Only Minnesota resident data from Minnesota death certificate records are included in the analysis; this excludes out-of-state deaths. Before 2005, ED visits did not include out-of-state ED visits for Minnesota residents. Hospitalization and ED visit rates for counties in which residents are likely to cross state lines for care may be underestimated. Rates for counties whose residents are likely to visit hospitals that do not submit data to the Minnesota Hospital Association (e.g., Veteran's Administration or Indian Health Services hospitals) may also be artificially low.

• Multiple hospital or emergency department admissions by the same patient cannot be identified, and are not excluded.

• Heat-related illness can exacerbate a number of chronic diseases and conditions, yet in a heat wave many of these conditions often are not attributed to heat exposure. This data only captures heat health outcomes that have been coded as attributed to heat.

• Since only people with the most severe or acute symptoms of heat-related illness are hospitalized, treated at the ED, or die, these data are not appropriate for estimating the total burden of heat-related illness in a population. The actual number of Minnesotans who experience heat-related illness is unknown. Heat-related illness is not currently a reportable condition in Minnesota.

• Mortality rates were not calculated due to the low number of deaths attributed to heat in Minnesota.

• Modeled data performs relatively well in estimating temperature, however, the estimates may differ when compared to weather station-based observations. The differences vary by region and some of these differences are expected from a meteorological perspective. As a result, an area may be described as having higher or lower temperatures than actually occurred.

• County-level estimates of temperature and heat index are obtained by processing modeled data, which are available by 1/8th-degree grid. The process of converting grid-level data to county-level estimates using a population-weighted approach may lead to potential misclassification of temperature and heat index for some areas.

• Values for heat index are not calculated for days with a maximum daily temperature less than 80 degrees Fahrenheit resulting in some missing values.

To learn more about heat-related illness and hot weather, visit Extreme Heat Events.

For more information about the heat-related illness data and measures, contact the MN Data Access Portal.