Wisconsin Communicable Disease Surveillance Data

Communicable diseases overview

This data visualization allows users to access the combined number of all reportable communicable diseases each year since 2010, as well as the 20 most frequently reported diseases for the selected year.

This tab displays the 20 most frequently reported communicable diseases for the selected year and the combined number of all reported communicable diseases for the year. The year for the 20 most frequently reported diseases can be changed using the drop-down menu located at the top left of the dashboard. Hovering over the blue bars will also display the rate of cases per 100,000 Wisconsin residents during that year.

This tab also displays cases by year. The dark blue bars represent all reported cases except cases of COVID-19. The gray bars represent the total number of COVID-19 cases reported during 2020– 2023 when individual cases of COVID-19 were reportable. Since November 2023, only cases of COVID-19-associated hospitalizations and COVID-19-associated pediatric deaths have been reportable. Hovering over the blue and gray bars will also display the case counts.

Disease-specific data

This tab allows users to select a specific reportable communicable disease by changing the disease name in the drop-down located at the top of the dashboard. The first graph displays the annual number of cases of the selected disease since 2010. Hovering over the blue bars will also display the rate of cases per 100,000 Wisconsin residents during each year. Based on the selected disease, the visualization may also include additional data-specific notes. These notes usually pertain to surveillance case definition changes that may impact case numbers. Conditions that were reportable but had no cases reported for a given year are displayed as zero in the cases by year graph. Case counts are blank if the condition had not yet been identified or was not reportable. For example, COVID-19 displays blanks for 2010–2019 before the condition was recognized and in 2024 when it was no longer reportable.

This tab also displays a summary of cases for the most recent five-year period, including the total cases, cases by year, cases by month, and the total number of hospitalizations and deaths. Cases by month are displayed because some conditions have strong seasonal patterns and other conditions occur without seasonal trends. Recognizing if a seasonal pattern occurs can help in understanding when risk may be higher. Hospitalization and death data can help show severity of disease.

Additionally, this tab includes a brief description of each disease or condition. Hover over "learn more about this disease" to read the brief description of each condition. There is also a link to the disease-specific webpage where users can find more detailed information about the disease and additional data and statistics for some conditions.

Annual case counts table

This summary table allows users to access the number of cases of all reportable communicable diseases each year from 2010– 2024 by disease category. Conditions that were reportable but had no cases reported for a given year are displayed as zero. Case counts are blank if the condition had not yet been identified or was not reportable. Users can download an Excel file with annual case counts by using the download file option at the bottom of this tab.

Data source

The data summarized on this dashboard are obtained from the Wisconsin Electronic Disease Surveillance System (WEDSS). WEDSS is a secure, web-based system designed to facilitate reporting, investigation, and surveillance of communicable diseases in Wisconsin. Most data are collected through routine, passive surveillance. The WEDSS reporting network is made up of institutions that treat patients or test specimens, including physicians, infection preventionists, laboratorians, and other health care providers.

Annual case rates are calculated using the estimated Wisconsin population provided by the Wisconsin Interactive Statistics on Health (WISH) Query System: Population Module.

Case definitions and reportable conditions

These visualizations summarize the burden of reportable communicable diseases meeting case definitions established by the Wisconsin Department of Health Services (DHS) and, when also nationally notifiable, the CDC (Centers for Disease Control and Prevention) and the Council of State and Territorial Epidemiologists (CSTE).

Wisconsin-specific case definitions can be found in guidance available on the DHS website for each disease and on the DHS Disease Reporting webpage. Requirements for the timing of reporting, once the disease or condition is recognized or suspected, vary by disease. General reporting requirements are described in Wis. Stat. ch. 252. A complete list of reportable conditions and the specific reporting requirements are described in Wis. Admin. Code ch. DHS 145 Control of Communicable Diseases.

Enumerated year

For most diseases, cases are enumerated and displayed in the visualizations based on the date of illness onset. For cases without an illness onset date reported in WEDSS, the date of specimen collection, test result, or report date, whichever is earliest, is used to enumerate the case.

For the following diseases, cases are enumerated using a different method than previously described. For TB cases, the case year is determined by date of a confirmatory diagnostic test. For prion disease cases, the case year is determined based on the date of death. For invasive bacterial diseases, meningococcal disease, invasive Haemophilus influenzae, invasive Streptococcus pneumoniae, and group A and B streptococcal invasive diseases, the date of first positive specimen collection is used.

This dashboard uses calendar year for annual case counts and does not use the MMWR year, which is the standard for data displayed by the CDC.

Hospitalization and death information

Public health surveillance for diseases and conditions does not always include active collection and documentation of hospitalization or death information in WEDSS. Data are displayed when available, but these data are not complete for all conditions. Additionally, any deaths or hospitalizations that occur much after the diagnosis and report of a particular disease may not be captured in these data since passive surveillance generally does not include long-term follow-up after a case is diagnosed and reported to public health. Hospitalization and death data are not provided in this visualization for hepatitis B, hepatitis C, and HIV.

Annual case rate

The annual case rate is determined by dividing the annual case count by the Wisconsin population for that year and then multiplying by 100,000. This generates the rate or number of people with a specific disease during that year if there were 100,000 residents in the state. Rates are a way to standardize and compare the frequency of disease occurrence among different size populations. This can help when comparing across years when the state population changes or comparing Wisconsin data with national data. Data in these dashboards has not been standardized by age.

Data shown are subject to change

Some examples of corrections or updates that affect presented data would include the delayed submission of a disease report, updating an onset date, correction to laboratory results, or correction of a patient’s address to a different state.

There may also be small differences between data summarized on these dashboards compared to other dashboards, static reports, or documents released by disease programs. There are multiple factors that can influence data discrepancies or differences in case counts. For example, factors include if programs use different case classification filters (such as confirmed cases only); if different dates are used for enumeration; if data are extracted at different timepoints; if the data source is different than WEDSS (for example, hospital discharge or vital records data); or if provisional data are displayed.

Data updates and downloads

Data will be updated annually in the fall and will provide data for cases that occurred during the previous calendar year. Users can download an Excel file with annual case counts by using the download file option at the bottom of the "Annual Case Counts Table" dashboard tab.

Questions?

For questions about the dashboard or data, email the DHS Bureau of Communicable Diseases at DHSDPHBCD@dhs.wisconsin.gov.