About the heat-related illness data and hot weather data

  • 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 measure is going up or down over time.
  • 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.
  • 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.
  • 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.

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.


  • 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.
  Code Description
  X30 Exposure to excessive natural heat
  T67.0 Heat stroke and sunstroke
  T67.1 Heat syncope (fainting)
  T67.2 Heat cramps
  T67.3  Heat exhaustion w/ water depletion
  T67.4  Heat exhaustion from salt depletion
  T67.5  Heat exhaustion, unspecified
  T67.6 Heat fatigue, transient
  T67.7 Heat edema (swelling)
  T67.8 Other unspecified heat effects
  T67.9 Unspecified effects of heat and light


  • The number indicates the total number of hospitalizations, ED visits, or deaths.
  • To protect an individual's privacy, hospitalizations and ED visit counts from 1 to 5 are suppressed if the underlying population is less than or equal to 100,000.


  • A rate is a ratio between two measures with different units. In our analysis a rate is calculated using a numerator (the number of heat-related illness hospitalizations, ED visits, or deaths during a period of time) divided by a denominator (the number of people at risk in a population during the same period of time). This fraction is then multiplied by 100,000. Mid-year Minnesota population estimates from the U.S. Census Bureau are used to calculate a rate.
  • To protect an individual's privacy, rates based on hospitalization or ED visits counts from 1 to 5 are suppressed if the underlying population is less than or equal to 100,000.
  • Rates based on counts of 20 or less are flagged as unstable and should be interpreted with caution. These rates are unstable because they can change dramatically with the addition or subtraction of one case.
    • An age-adjusted rate is an overall summary measure that helps to control for age differences between populations. A weighted average, called the "direct method," is used to adjust for age. The U.S. 2000 standard population is used as the basis for weight calculations.
    • Age-adjusted rates are useful when comparing the rates of two population groups that have different age distributions.
  • 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 the heat-related illness data and measures provided by the MN Environmental Public Health Tracking Program, contact MNPH Data Access.