COVID-19: Data 101

Learn about our data

We strive for transparency and accuracy in our data, and 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 consolidation of case records,
  • Update of case's demographic information from missing or unknown to complete information.

Interpreting data

Download 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: 

The Data Dictionary (PDF)  can also be downloaded that will provide more information about the different elements available to download in the data listed above.

Some DHS COVID-19 data is available for download directly from the visualization on the page. You can click on the visualization and then click "Download" at the bottom of the visualization. Next, select either "Data" or "Crosstab" from the corresponding pop-up to see summaries of the data in the visualization. If the "Data" or "Crosstab" is not available (gray), the data is not available for download at this time, but may be downloaded as a "PDF", "Image", or "PowerPoint".

Download content from Tableau

Case data

All data are laboratory-confirmed cases of COVID-19 that we extract from our live Wisconsin Electronic Disease Surveillance System (WEDSS) and freeze once a day. These numbers are the official state numbers, though counties may report their own totals independent of DHS. Combining the DHS and local totals may result in inaccurate totals.

The number of people with negative test results includes only Wisconsin residents who had negative test results reported electronically to DHS or entered manually into the WEDSS electronic laboratory module. As a result, this number underestimates the total number of Wisconsin residents with negative test results.

Probable cases

A person is counted as a COVID-19 probable case if they are not positive by a confirmatory laboratory test (for example, a test that detects the virus in the nose or throat), but have a combination of other factors. These other factors are symptoms of COVID-19, exposure to COVID-19 (for example, being a contact of someone who has laboratory confirmed COVID-19), or a positive non-confirmatory laboratory test (for example, a blood test that detects antibodies against the virus causing COVID-19).

A detailed surveillance case definition for COVID-19 probable cases (used by public health and not to be used for making diagnostic or clinical decision) is available under Reporting and Surveillance Guidance on the DHS COVID-19 Health Care Providers webpage.

Group housing status

Long-term care facilities include skilled nursing facilities (nursing homes) and assisted living facilities (community-based residential facilities and residential care apartment complexes).

Group housing facilities include correctional facilities, homeless shelters, dormitories, and group homes.

The data on group housing is unknown at this time for a portion of cases because these data have only been systematically collected since April 8, 2020. However, any COVID cases who were part of an outbreak investigation in a long-term care or other group housing facility prior to April 8 are classified under the appropriate group setting category (and are not included in the unknown category).

Health care workers

Data on COVID-19 cases who are health care workers represents a broad range of occupations in the health care field, including nurses, physicians, surgeons, physician assistants, health care support staff, emergency medical technicians and paramedics, dentists and other dental health workers, and pharmacists.

Recovery status

The number of patients recovered from COVID-19 is defined as the number of confirmed cases who are currently alive based on Wisconsin state vital records system data and had one or more of the following:

  • Documentation of resolved symptoms
  • Documentation of release from public health isolation
  • 30 days since symptom onset or diagnosis*

Active cases include COVID-19 cases who were diagnosed in the last 30 days, are not known to have died, and do not yet meet the definition of having recovered.

*Our data indicate that the vast majority of reported cases who recovered did so within 30 days. Rarely, more than 30 days were required to recover. As a result, a very small number of cases who are still recovering might be included in the 'Recovered' category.

COVID-19 activity levels

Regions and counties are classified as high, medium, or low activity levels for disease spread by combining the case burden and trajectory indicators. Burden (case rate) and trajectory (case change) indicators are based on confirmed COVID-19 cases. The COVID-19 activity level maps burden and trajectory indicators based on whether the burden status is low, moderate, moderately high, or high and whether trajectory status is significantly shrinking, growing, or has no statistically significant change.

Burden (case rate)

Burden is the total number of cases per 100,000 Wisconsin residents in the last two weeks.

Burden status Value (per 100,000 Wisconsin residents in the past two weeks)
Low Case rate is less than or equal to 10.
Moderate Case rate is greater than 10, but less than or equal to 50.
Moderately High Case rate is greater than 50, but less than or equal to 100.
High Case rate is greater than 100.

Trajectory (percent case change)

Trajectory is the percent change from previous to current week and p-value (indicates statistical significance) from a test against the percent change equal to zero.

Trajectory status Value (change from prior 7-day period to most recent 7-day period)
Shrinking Percent change in cases is less than or equal to negative 10 percent, and p-value is less than 0.025.
Growing Percent change in cases is greater than or equal to 10 percent, and p-value is less than 0.025.
No Significant Change Any other conditions besides those that meet the "shrinking" or "growing" statuses described above.

Activity level

Activity level is a summary indicator based on whether the burden (case rate) status and the trajectory (case change) status as defined in the tables above.

Burden Trajectory Activity Level
Low Shrinking Low
Low No Significant Change Low

 

Burden Trajectory Activity Level
Low Growing Medium
Moderate Shrinking Medium
Moderate No Significant Change Medium
Moderately High Shrinking Medium

 

Burden Trajectory Activity Level
Moderate Growing High
Moderately High No Significant Change High
Moderately High Growing High
High Shrinking High
High No Significant Change High
High Growing High

 

 

Death data

Deaths must be reported by health care providers, medical examiners/coroners, and recorded by local health departments in order to be counted.

Probable deaths

A COVID-19 probable death is a COVID-19 probable case who died, or a person's death certificate lists COVID-19 (or the virus causing COVID-19) as a cause of death or a significant condition contributing to death.

Group housing status

Long-term care facilities include skilled nursing facilities (nursing homes) and assisted living facilities (community-based residential facilities and residential care apartment complexes).

Group housing facilities include correctional facilities, homeless shelters, dormitories, and group homes.

The data on group housing is unknown at this time for a portion of deaths because these data have only been systematically collected since April 8, 2020. However, any COVID cases who were part of an outbreak investigation in a long-term care or other group housing facility prior to April 8 are classified under the appropriate group setting category (and are not included in the unknown category).

Facility-wide investigations

A single confirmed case in the following setting initiates a facility-wide public health investigation:

  • Long-term care facilities include skilled nursing facilities (nursing homes) and assisted living facilities (community-based residential facilities and residential care apartment complexes).

Two or more confirmed cases in the following settings initiate a facility-wide public health investigation:

  • Group housing facilities include correctional facilities, homeless shelters, dormitories, and group homes.
  • Health care facilities include hospitals, clinics, dialysis centers, hospice, and in-home care.
  • Workplace (non-health care) settings include manufacturing and production facilities, distribution facilities, offices, and other indoor workplaces.
  • Other settings include adult or child day care centers, restaurants, event spaces, and religious settings.

A case investigation and contact tracing is conducted with all people reported with COVID-19, regardless of setting.

Facility-wide and outbreak investigations are considered closed when two maximum incubation periods have passed since the last possible exposure to a COVID-19 case in the facility without any new cases. For COVID-19, two maximum incubation periods are 28 days (maximum incubation period is 14 days).

Detecting COVID-19 in a nursing home is an indicator that the nursing home is following proper notification procedures and working with public health experts to test and protect their residents and employees by using appropriate isolation and infection control practices. Proactive testing helps address outbreaks early on while they’re easier to isolate and manage.

As individual cases are investigated by public health, there may be corrections to the status and details of cases that result in changes to this information. Also below is a list of nursing homes with active COVID-19 facility-wide public health investigations in Wisconsin by county.

Hospital Capabilities

As we continue to fight COVID-19 in our state, one of our main goals is to not overwhelm the hospitals. We must protect the capacity of our healthcare system and of our frontline health care workers, so that the amount of manpower and beds that we have in our state are able to treat and serve all Wisconsinites who need hospitalization from COVID-19. That’s key, because if we don’t have capacity in our healthcare system, we cannot take care of our families, friends, or neighbors who may become ill with this virus, or patients with needs that are not COVID-related.

Ventilators

The amount of ventilators available gives us an idea of how well equipped our hospital systems are to not only handle COVID-19 patients, but other patients who may also need ventilation. For ventilator use, we are currently reporting the total of all machines capable of provide ventilation. This is done in line with new guidance from the Federal Department of Health and Human Services (HHS).

Previously, we would report hospital ventilator supply only for “general use bedside ventilators,” which are most common for treating COVID-19 patients in need. However, when necessary, there are additional ventilator machines that can be used. By capturing the total amount of ventilators statewide, we are able to get a better measure of hospital capabilities should a growing amount of ventilators be needed by COVID-19 patients. You may notice that the proportion of ventilators available is now higher than before—this is because we are looking at how many ventilators are available compared to all the different ventilator machines. Before we were only comparing available ventilators to the total of “general use bedside ventilators” available. 

Ventilator capacity includes the use of all of the following types of equipment in the hospitals: 

  • General Use Bedside Ventilators
  • Anesthesia Machines
  • BiPAP Machines
  • ECMO Machines
  • Home Use Ventilators
  • Oscillators / High Frequency Ventilators
  • Weight Limited NICU Bedside Ventilators

Methods of reporting COVID-19 data

Epidemic curves

An epidemic curves (or "epi curve") is used to track the number of illnesses over time and see when peaks of illnesses occur.

A cumulative epidemic curve shows the total (cumulative) number of confirmed cases, regardless of whether the cases have recovered. The cumulative epidemic curve represents how COVID-19 is spreading and expanding statewide and by county over time. An upward trend in the curve shows a time period where the number of cases are growing. A steeper curve in the chart signals that cases are growing at a higher rate.

A cumulative mortality curve shows the total (cumulative) number of deaths among confirmed cases statewide and by county over time. An upward trend in the curve shows a time period where the number of COVID-19-related deaths are increasing. A steeper curve in the chart signals a higher rate of deaths. 

Preliminary data

Some data we report on for COVID-19 has a data lag time, and data during the most recent two weeks will be highlighted as preliminary data.

When people have an acute illness, such as COVID-19, it may take several days for them to see a doctor or be tested. It also takes time for the tests to be completed and the results to be sent to public health to be included in case counts.

It also takes time for patient deaths to be reported to public health and to be included in death counts.

Symptom onset date

A symptom onset date represents when an individual's symptoms began. Symptom onset date is more meaningful than using the date when the case was reported because it represents when illnesses occurred, instead of when the person was tested and the result was reported to public health.

If symptom onset date is missing or the patient did not have symptoms, we report data by diagnosis date.

Last Revised: July 22, 2020

 RESPONSE RESOURCES FOR WISCONSINITES — www.dhs.wisconsin.gov/covid-19/help.htm