Environmental Public Health Tracking: Asthma Data

Asthma is a disease that affects a person’s breathing and may limit their ability to get fresh air to their lungs.

Wisconsin Tracking provides data and information on asthma.

Read the frequently asked questions below for more information about asthma.

Access the asthma data

Girl uses an inhaler

Interested in environmental health data?

Join the environmental health listserv by sending an email to DHS Environmental Public Health Tracking with the subject line "Join envhealth listserv."

Frequently asked questions

What is asthma?

Asthma is a disease that affects a person’s breathing and can make it hard to get oxygen to their lungs. For people with asthma, the inside of their airways can swell or become irritated and inflamed.  This irritation leads to wheezing and coughing.

To learn more about asthma, visit the Wisconsin Asthma Program.

What causes asthma?

The root causes of asthma are not entirely understood.  However, specific triggers are known to cause breathing problems for people with asthma. More information about asthma is available from the Wisconsin Asthma Program.

How is asthma related to the environment?

There is strong evidence linking asthma and being in contact with allergens, tobacco smoke, and indoor and outdoor air pollution. Research shows a connection between increased hospital admissions for asthma and particulate matter, a type of outdoor air pollution.

Why does Wisconsin Tracking track asthma?

Gathering data on asthma trends allows  public health professionals to  identify high-risk groups, evaluate current prevention efforts, and plan programs and policies to reduce the burden of asthma.

With Wisconsin Tracking data, public health professionals can answer questions such as:

  • How many people go to the emergency room for asthma each month?

  • Is there a relationship between the season and how many people visit the ER or are hospitalized for asthma?

  • How do hospitalizations or ER visits for asthma differ between zip codes and counties?

  • Are there disparities in asthma hospitalizations or ER visits among different age groups, races, ethnicities, and genders?

  • Which populations are in greatest need of programs, policies, or other interventions to address asthma?

  • How do levels of certain environmental exposures, such as particulate matter, relate to asthma hospitalizations and ER visits?

What is the data source?

The source of these data is the Wisconsin Hospital Association Information Center, Inc.  To calculate rates, these data are combined with population data from the National Center for Health Statistics.

Which measures does Wisconsin Tracking have for asthma?

  • Annual number of asthma hospitalizations and ER visits by age, gender, race/ethnicity, and location
  • Monthly average of hospitalizations and ER visits
  • Monthly maximum daily number of hospitalizations and ER visits
  • Monthly minimum daily number of hospitalizations and ER visits
  • Daily number of hospitalizations and ER visits
  • Annual unadjusted (crude) rate for asthma hospitalizations and ER visits, by age, gender, race/ethnicity, and location
  • Annual age-specific rates of asthma hospitalizations and ER visits, by age, gender, race/ethnicity, and location
  • Annual age-adjusted rate of asthma hospitalizations and ER visits, by age, gender, race/ethnicity, and location

What are some considerations for interpreting the data?

  • Because these data are based on hospital admissions and emergency department visits, some people who experience symptoms are not included. These people include: those who do not receive medical care, those whose care does not result in hospitalization, and those who die in settings such as ambulances, nursing homes, or at home.
  • Data from years 2000 to present include hospitalizations among Wisconsin residents who were treated in Minnesota hospitals.  In addition, data from years 2005 to present include hospitalizations among Wisconsin residents who were treated in Iowa hospitals.
  • Data from years 2002 to present include emergency department visits among Wisconsin residents who were seen in Minnesota hospitals.  In addition, data from years 2005 to present include emergency department visits among Wisconsin residents who were treated in Iowa hospitals.
  • These data do not include inpatient admissions or emergency department visits at hospitals owned by the federal government. This includes Veterans Administration hospitals.
  • Data users should keep in mind that many factors contribute to a disease. These factors should be considered when interpreting the data.  Factors include:
    • Demographics (race, gender, age)
    • Socioeconomic status (income level, education)
    • Geography (rural, urban)
    • Changes in the medical field (diagnosis patterns, reporting requirements)
    • Individual behavior (diet, smoking)

Where can I learn more about asthma?

Asthma data details

Data Details

Asthma emergency department visits

Number of emergency department visits for asthma

These data include emergency department visits for asthma and are collected from emergency room visit discharge records. Emergency department visits resulting in subsequent hospitalization are also included. Federally funded hospitals (for example, Veteran's Administration [VA] hospitals, which are exempt from state reporting requirements) are not included in these data. This measure includes emergency department visits with an ICD-9 code of 493 or ICD-10 code of J45 in the principal diagnosis field. Data are suppressed for counties with fewer than five visits to protect confidentiality. However, counties with zero cases are not suppressed. Please note that counts are a statistically-limited way to consider emergency department visits because they do not allow for accurate comparison between counties. Counties with higher populations, such as Milwaukee, will have more emergency department visits simply because they have more people. An age-adjusted rate is a better measure for true comparison between counties.

Prior to 2018, the county variable in the emergency department (ED) data was assigned based on the zip code of the residence of the patient. In cases where a zip code spanned more than one county, the ED visit was placed into the county with the higher population. Beginning in 2018, geocoded data became available in Wisconsin ED visit data, which allows for a more accurate determination of county of residence. The new block group variable is the geocoded latitude/longitude of the patient’s residential address. The first five digits of the block group variable are used to determine the Wisconsin county. Due to this change, caution should be used when comparing county-level data prior to 2018 with data from 2018 onward.

Crude rates of emergency department visits for asthma per 10,000 people

These data include emergency department visits for asthma and are collected from emergency room visit discharge records. Emergency department visits resulting in subsequent hospitalization are also included. Federally funded hospitals (for example, Veteran's Administration [VA] hospitals, which are exempt from state reporting requirements) are not included in these data. This measure includes emergency department visits with an ICD-9 code of 493 or ICD-10 code of J45 in the principal diagnosis field. Data are suppressed for counties with fewer than five visits to protect confidentiality. However, counties with zero cases are not suppressed. The crude rate is the number of emergency department visits divided by the total number of people in the area of interest (for example, a county). Population of interest is derived from census data. This is expressed as a number per unit population such as "per 10,000 population." Crude rates do not take into account the differences in age distributions across counties and are therefore subject to bias. Use age-adjusted rates for a better standardized measure.

Prior to 2018, the county variable in the emergency department (ED) data was assigned based on the zip code of the residence of the patient. In cases where a zip code spanned more than one county, the ED visit was placed into the county with the higher population. Beginning in 2018, geocoded data became available in Wisconsin ED visit data, which allows for a more accurate determination of county of residence. The new block group variable is the geocoded latitude/longitude of the patient’s residential address. The first five digits of the block group variable are used to determine the Wisconsin county. Due to this change, caution should be used when comparing county-level data prior to 2018 with data from 2018 onward.

Asthma emergency department visits age-adjusted rates per 10,000 people

These data include emergency department visits for asthma and are collected from emergency room visit discharge records. Emergency department visits resulting in subsequent hospitalization are also included. Federally funded hospitals (for example, Veteran's Administration [VA] hospitals, which are exempt from state reporting requirements) are not included in these data. This measure includes emergency department visits with an ICD-9 code of 493 or ICD-10 code of J45 in the principal diagnosis field. Data are suppressed for counties with fewer than five visits to protect confidentiality and improve rate stability. However, counties with zero cases are not suppressed. An age-adjusted rate is a rate that is statistically modified to eliminate the potential biasing effect of different age distributions across different populations. In other words, the age-adjusted rate accounts for the possibility that emergency department visits for asthma may be more frequent among younger individuals and some counties have more younger individuals than others. Direct age-adjustment is conducted using the 2000 U.S. standard population.

Prior to 2018, the county variable in the emergency department (ED) data was assigned based on the zip code of the residence of the patient. In cases where a zip code spanned more than one county, the ED visit was placed into the county with the higher population. Beginning in 2018, geocoded data became available in Wisconsin ED visit data, which allows for a more accurate determination of county of residence. The new block group variable is the geocoded latitude/longitude of the patient’s residential address. The first five digits of the block group variable are used to determine the Wisconsin county. Due to this change, caution should be used when comparing county-level data prior to 2018 with data from 2018 onward.

Asthma hospitalizations

Number of hospitalizations for asthma

These data include hospitalizations for asthma and are collected from inpatient hospital discharge records. This measure includes hospitalizations with an ICD-9 code of 493 or ICD-10 code of J45 in the principal diagnosis field. Data are suppressed for counties with fewer than five visits to protect confidentiality. However, counties with zero cases are not suppressed. Please note that counts are a statistically limited way to consider emergency department visits because they do not allow for accurate comparison between counties. Counties with higher populations, such as Milwaukee, will have more hospitalizations simply because they have more people. An age-adjusted rate is a better measure for true comparison between counties.

Prior to 2018, the county variable in the hospitalization data was assigned based on the zip code of the residence of the patient. In cases where a zip code spanned more than one county, the hospitalization was placed into the county with the higher population. Beginning in 2018, geocoded data became available in Wisconsin hospitalization data, which allows for a more accurate determination of county of residence. The new block group variable is the geocoded latitude/longitude of the patient’s residential address. The first five digits of the block group variable are used to determine the Wisconsin county. Due to this change, caution should be used when comparing county-level data prior to 2018 with data from 2018 onward.

Crude rates of hospitalizations for asthma per 10,000 people

These data include hospitalizations for asthma and are collected from inpatient hospital discharge records. This measure includes hospitalizations with an ICD-9 code of 493 or ICD-10 code of J45 in the principal diagnosis field. Data are suppressed for counties with fewer than five visits to protect confidentiality. However, counties with zero cases are not suppressed. The crude rate is the number of hospitalizations divided by the total number of people in the population of interest (for example, a county). This is expressed as a number per unit population, such as "per 10,000 population." A crude rate does not take into account the differences in age distributions across counties and are therefore subject to bias. Use age-adjusted rates for a better standardized measure.

Prior to 2018, the county variable in the hospitalization data was assigned based on the zip code of the residence of the patient. In cases where a zip code spanned more than one county, the hospitalization was placed into the county with the higher population. Beginning in 2018, geocoded data became available in Wisconsin hospitalization data, which allows for a more accurate determination of county of residence. The new block group variable is the geocoded latitude/longitude of the patient’s residential address. The first five digits of the block group variable are used to determine the Wisconsin county. Due to this change, caution should be used when comparing county-level data prior to 2018 with data from 2018 onward.

Asthma hospitalizations age-adjusted rates per 10,000 people

These data include hospitalizations for asthma and are collected from inpatient hospital discharge records. This measure includes hospitalizations with an ICD-9 code of 493 or ICD-10 code of J45 in the principal diagnosis field. Data are suppresses data for counties with fewer than five visits per 10,000 to protect confidentiality. However, counties with zero cases are not suppressed. An age-adjusted rate is a rate that is statistically modified to eliminate the potential biasing effect of different age distributions across different populations. In other words, the age-adjusted rate accounts for the possibility that emergency department visits for asthma may be more frequent among younger individuals and some counties have more younger individuals than others. Direct age-adjustment is conducted using the 2000 U.S. standard population.

Prior to 2018, the county variable in the hospitalization data was assigned based on the zip code of the residence of the patient. In cases where a zip code spanned more than one county, the hospitalization was placed into the county with the higher population. Beginning in 2018, geocoded data became available in Wisconsin hospitalization data, which allows for a more accurate determination of county of residence. The new block group variable is the geocoded latitude/longitude of the patient’s residential address. The first five digits of the block group variable are used to determine the Wisconsin county. Due to this change, caution should be used when comparing county-level data prior to 2018 with data from 2018 onward.

Average daily count

These data include hospitalizations for asthma and are collected from inpatient hospital discharge records. This measure includes hospitalizations with an ICD-9 code of 493 or ICD-10 code of J45. Average Daily Count was calculated by dividing the monthly count by the number of days in that respective month.

Glossary and definitions of terms

Explore definitions and explanations of terminology found on the portal, like age-adjusted rate and confidence intervals.

Last Revised: August 1, 2022