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.
Cases, Deaths, and Hospitalizations
Why have DHS's data quality assurance efforts impacted case and death data?
In recent weeks, DHS has been able to ramp up data quality assurance efforts. This effort includes merging duplicate case records and correcting disease status in the Wisconsin Electronic Disease Surveillance System (WEDSS). A majority of the changes are a result of case status being corrected from "confirmed" to "probable". Confirmed and probable cases are classified according to a standardized case definition (for example, based on laboratory testing). However, for the purposes of public health follow-up, the health recommendations for confirmed and probable cases are the same. Quality assurance efforts are a critical piece of our efforts to finalize COVID-19 cases or deaths, as well as those showing newly reported numbers each day may appear lower than expected – in some counties, substantially lower or even negative. As a result, numbers including COVID-19 burden and trajectory on our Disease Activity dashboard will appear differently. This is because any corrected numbers from our quality assurance efforts are reflected in the most recent reporting date.
Charts showing confirmed cases and deaths by group housing setting are also undergoing quality assurance efforts. This involves matching patient addresses to the Division of Quality Assurance long-term care facility addresses to assign group housing setting to long-term care facility if it was originally "unknown" in WEDSS. We also review deaths abstracts to reduce the number with unknown group living setting. This data quality assurance project is ongoing and is helping to reduce the number of "unknowns" in our group housing charts.
DHS has been performing quality assurance throughout the pandemic. As case counts have decreased, quality assurance efforts have become more noticeable.
For the most accurate picture of COVID-19 in Wisconsin, reference our data visualizations, that show confirmed and probable cases by date of onset or diagnoses and deaths by date of death. These are more meaningful metrics than those showing the dates reported to DHS – which may be subject to change as public health follow-up continues and data are corrected.
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.
Are mutations among viruses common?
Yes. Viruses constantly change through mutation and new variants are expected to occur over time. Multiple variants of the SARS-CoV-2 virus, the virus that causes COVID-19, have been documented in the United States and globally during this pandemic. Most variants do not change how the virus behaves and may disappear.
What are the consequences of a virus that spreads more easily?
A higher rate of transmission could lead to more cases, which would increase the number of people who experience moderate to severe disease or require hospitalization. It may also increase the number of those who need to be vaccinated to fully disrupt community transmission when vaccines become widely available.
What is WIR?
The Wisconsin Immunization Registry (WIR) is an online system that tracks immunizations given in health care settings into one record for Wisconsin citizens. Due to the majority of health care organizations that report, WIR has the most up-to-date records for Wisconsin patients. For more information on how to access your own vaccine record, visit the DHS WIR webpage.
Where does the data come from?
WIR receives information from the Wisconsin Vital Statistics program, doctor's offices, hospitals, employee health sites, schools, health maintenance organizations, Medicaid, the Wisconsin Lead Program, and Minnesota and Michigan's immunization registries.
There are roughly 3,800 health care provider locations and 3,200 schools and school districts across Wisconsin that report to WIR. Many of these health care providers send data to WIR through data exchange. With data exchange, as soon as an immunization is entered into a chart at the doctor's office, it is automatically sent to WIR. Other health care providers manually enter data into the online system or submit immunizations through a flat file, which is a formatted file with multiple individuals that can be uploaded to WIR.
Typically, anyone that does not want their immunization history shared in WIR can request to opt-out of the database. However, this option is not available for COVID-19 vaccination due to Centers for Disease Control and Prevention (CDC) guidelines.
Are providers required to report immunizations to WIR?
Reporting to WIR is not mandatory unless the provider is part of the Vaccines for Children (VFC) and/or Vaccines for Adults (VFA) programs. Pharmacists who immunize children aged 6-18 have been required since 2015 to submit immunization data within 7 days of administering a vaccine.
The CDC also mandates reporting of all COVID-19 vaccination administration to WIR. CDC has recommended all COVID-19 immunizations administered be submitted to their state's registry within 24 hours.
Does the system record the location where the person was vaccinated or their home address?
Both. It is important that we know where a person went to get vaccinated and their primary address. Knowing where someone went to get vaccinated can help us determine how to best distribute doses. Vaccine coverage data is calculated using people's primary addresses. This is why vaccine coverage rates can sometimes fluctuate; if enough people move to a different area, they now contribute to the vaccine coverage in that area and no longer contribute to the coverage at their old address.
Why is it that sometimes the number of Pfizer or Moderna doses administered might go down from one day to the next?
Vaccinations come to WIR either directly from the location's medical chart system or from staff manually entering vaccine data to WIR. With both processes, there is some form of manual entry that occurs and is subject to human error. As such, it is reasonable that entry mistakes can occur and may affect the data that is reported to the website.
As individual vaccinations are investigated by public health, there may be corrections or updates to the details reported in WIR that result in changes to this information. Some examples of corrections or updates that may lead to changes to our data, such as the number of doses administered going up or down, include:
- Removing duplicates or merging and consolidation of records
- Updating a patient's address to a different county or state
- Updates or corrections to the manufacturer code reported in WIR
- Updates or corrections to a patient's information in WIR
Why is the data on the CDC page different than what is on the Wisconsin vaccine data page?
Data on this page may differ from data reported on the CDC COVID Data Tracker due to the fact that data may be updated on different schedules and reflect data "as of" different dates or times of day. There may also be a delay between the time a vaccination record appears in the state system and when it is received by CDC.
In addition, the CDC requires we report the newest data that we have available. Unfortunately, this does not allow the necessary time to check the data for accuracy and reach out to providers to investigate any entry errors. At this time there is no way for us to submit corrections to the CDC. As such, the CDC data will never align fully with the data we report on the COVID-19 vaccine data page.
How can I download DHS COVID-19 Data?
COVID-19 data is available for download in several formats from the DHS website. To download spatial and mapped 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).