Learn about our data
We strive for transparency and accuracy in our data. Below are answers to frequently asked questions about our data. There are also additional details on how to access and interpret the data on our website.
About our data: How do we measure this?
How does DHS collect information on cases of COVID-19?
Information on COVID-19 cases is collected through the standard communicable disease surveillance system used for all other reportable communicable diseases in Wisconsin. Laboratories and health care providers are required to report information (including the person’s name, birth date, address, type of test, test result) on cases of COVID-19 (and other reportable communicable diseases) to the health department. This information is most often transmitted to DHS and local health departments into the Wisconsin Electronic Disease Surveillance System (WEDSS) through an electronic submission or data feed. Sometimes information is also transmitted manually through faxes or phone calls.
After the information is received into WEDSS, local health departments attempt to contact the person (and in some cases the person’s health care provider) to gather more information. This includes getting details about the person’s illness (symptoms, whether hospitalization was required) and how the person might have become infected (travel history, any known contact with a COVID-19 case). For the purpose of contact investigating, this also means asking who the person had contact with before getting COVID-19. Local health departments or DHS contact tracing staff enter this information into WEDSS. It is not uncommon for information about cases to be delayed or incomplete in WEDSS. This is because public health may have trouble contacting the person with COVID-19 or the person might not provide all of the information required.
Based on the laboratory results and other available information, local health departments and DHS classify cases according to the standard, national COVID-19 case definition from the CDC.
Only cases with positive test results using a confirmatory diagnostic test that detect the genetic material of SARS-CoV-2, the virus that causes COVID-19, are classified as a confirmed case of COVID-19.
A case is classified as probable if they are not positive by a diagnostic, confirmatory test, but have met one of the following:
- Test positive using an antigen test method
- Have symptoms of COVID-19 AND known exposure to COVID-19 (for example, being a close contact of someone who was diagnosed with COVID-19)
- COVID-19 or SARS-CoV-2 is listed on the death certificate
A detailed surveillance case definition for COVID-19 probable cases (used by public health and not to be used for making diagnostic or clinical decisions) is available under Reporting and Surveillance Guidance on the COVID-19 Health Care Providers webpage.
Visit our disease reporting page to see the diseases and conditions that must be reported to public health. You can also learn more about case reporting methods and contact information.
If a person tests positive for COVID-19 more than once, are they included in the number of confirmed cases more than once?
No. The number of confirmed cases is the number of people diagnosed with COVID-19 using a diagnostic test (a test to detect the genetic material of SARS-CoV-2, the virus that causes COVID-19). If a person tests positive more than once, they are only included as a confirmed case once.
Why is it that the number of newly reported cases of COVID-19 can go up and down (for example, there can be 1,100 new cases reported on Tuesday, but only 700 new cases reported on Wednesday)? Are those changes from day-to-day important?
The number of newly reported COVID-19 cases can fluctuate from day-to-day depending on when the testing occurs and how the data are collected and processed in WEDSS. For example, less COVID-19 data are processed over the weekend compared to during the week. This often results in fewer new cases being reported on Mondays and more new cases being reported Tuesdays. Rather than focusing on the number of new cases on any given day, it is more important to monitor the overall trend in the number of new cases. For example, the "New confirmed COVID-19 cases by date confirmed, and 7-day average" chart includes a line of the 7-day average. This line smooths out these day-to-day fluctuations in the numbers of cases reported and more clearly shows the trend in new cases.
Why is it that sometimes the number of confirmed cases or deaths in a county might go down from one day to the next?
As individual cases are investigated by public health, there may be corrections to the status and details of cases or deaths that result in changes to this information. Some examples of corrections or updates that may lead to changes to our data, such as case and negative counts and deaths going up or down, include:
- Update or correction of case's address, resulting in a change to their location of residence to another county or state,
- Correction to laboratory result,
- Correction to a case's status from confirmed to unconfirmed (for example, if they were marked as confirmed because a blood test detecting antibodies was positive instead of a test detecting the virus causing COVID-19),
- De-duplication or merging and consolidating case records,
- Update of case's demographic information from missing or unknown to complete information.
Which deaths are counted as COVID-19 deaths?
DHS classifies deaths according to the national standard case definition outlined by the CDC and the Council of State and Territorial Epidemiologists (CSTE).
According to that definition, COVID-19 deaths are those that have a death certificate that lists COVID-19 disease or SARS-CoV-2 as an underlying cause of death or a significant condition contributing to death. Deaths must be reported by health care providers or medical examiners/coroners and recorded in WEDSS by local health departments in order to be counted as a COVID-19 death. Deaths among people with COVID-19 that were the result of non-COVID reasons (e.g., accident, overdose, etc.) are not included as a COVID-19 death.
If a person tests positive for COVID-19 and then dies of an accident (or other causes not related to COVID-19) are they considered a COVID-19 death?
No. If the death certificate indicates that the cause of death was a result of reasons not related to COVID-19 (for example, death related to an accident, overdose, or other non-COVID-related conditions) and COVID-19 is not listed on the death certificate as contributing to the death, the person is not included as a COVID-19 death.
If a person tests positive for COVID-19 during a visit to the emergency department and is not admitted to the hospital, are they considered a COVID-19 hospitalization?
No. Only persons who have documentation in WEDSS of being admitted to the hospital are considered a COVID-19 hospitalization. If a person is tested while in the emergency department and is not admitted, they are not considered a COVID-19 hospitalization.
How can I download DHS COVID-19 Data?
To download our data visit one of the following links:
- State data
- County data
- Census tract data
- Municipality data
- School district data
- Zip code data
- Disease activity and hospital capacity data
- Testing sites
The Data Dictionary (PDF) can also be downloaded. It provides more information about the different elements available to download in the data listed above.
All DHS COVID-19 data is available for download directly from the chart on the page. You can click on the chart and then click "Download" at the bottom of the chart (gray bar).