COVID-19: Disease Activity by Region and County

 

 

Understanding our data: What does disease activity mean?

There are many pieces of data that can help guide decisions on how to address COVID-19 in the community. The Disease Activity section provides a snapshot of what we can see from looking at confirmed cases (case activity levels). Beyond lab-confirmed cases, it also points to how many emergency department (ED) visits occur for COVID-19-like illnesses (CLI) and influenza-like illnesses (ILI). Looking at percent positive by test is a critical way to understand how prevalent the COVID-19 virus is in the community. A high percent positive likely indicates that there is undetected infection and not enough people are being tested. However, these data need to be looked at in conjunction with the other disease activity metrics – confirmed cases, CLI, and ILI – to truly understand the spread. Viewed together, these metrics show what we know about disease activity and how severely different communities are being affected by COVID-19 and other respiratory illnesses.

Please note that the Wisconsin Electronic Disease Surveillance (WEDSS) system underwent routine maintenance and enhancements over the weekend of October 16-18, 2020. Due to this temporary pause in reporting, multiple days of data were uploaded at once, affecting the single day count for the visualizations during that time.

About our data: How do we measure case activity?

How many people do we know have COVID-19 and is that number increasing?

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

Data source: Wisconsin Electronic Disease Surveillance System (WEDSS).

Data are confirmed cases of COVID-19 reported to WEDSS. Cases are classified using the national case definition established by the CDC. Confirmed cases are those that have positive results from diagnostic, confirmatory polymerase chain reaction (PCR) tests or nucleic acid amplification tests (NAT) that detect genetic material of SARS-CoV-2, the virus that causes COVID-19. Illnesses with only positive antigen or positive antibody test results do not meet the definition of confirmed and are not included in the number of confirmed cases.

There is a period of time between COVID-19 tests being conducted and a confirmed case being reported. Dates reported here are the "confirmed date", meaning the date that results confirmed by local health departments are posted to the DHS website. While all of the disease activity indicators (cases, CLI, and ILI) are pulled on the same day, using confirmed date for cases means that the date range is slightly different from CLI and ILI, which do not need to go through the same confirmation process and do not have an equivalent date.

Burden (case rate)

Burden is the total number of COVID-19 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, but less than or equal to 350.
Very High Case rate is greater than 350, but less than or equal to 1,000.
Critically High Case rate is greater than 1,000.

 

Trajectory (percent case change)

Trajectory is the percent case change from the previous to the current week and indicates whether the change is statistically significant.

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 is statistically significant (p-value is less than 0.025).
Growing Percent change in cases is greater than or equal to 10 percent, and is statistically significant (p-value is less than 0.025).
No Significant Change Any other conditions besides those that meet the "shrinking" or "growing" statuses described above.

 

Case activity level

The case activity level is a summary indicator combining burden and trajectory. The case activity level is either low, medium, high, very high, or critically high.

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

 

Burden Trajectory Activity level
Very High Shrinking Very High
Very High No Significant Change Very High
Very High Growing Very High

 

Burden Trajectory Activity level
Critically High Shrinking Critically High
Critically High No Significant Change Critically High
Critically High Growing Critically High

 

We plan to update our data each Wednesday by 5 p.m.

About our data: How do we measure percent positive by test?

What percent of COVID-19 tests have a positive result?

Data in this dashboard includes all Wisconsin residents tested in- and out-of-state. This figure includes data on diagnostics, confirmatory polymerase chain reaction (PCR) tests or nucleic acid amplification tests (NAT) that detect the genetic material of SARS-CoV-2, the virus that causes COVID-19. No antigen or antibody test results are included in this visualization.

For percent positive by test, data are calculated by counting each test, not each person getting tested, so a person is counted each time they have a test performed. Therefore, if they get multiple positive or negative results, they are counted each time they are tested, on the date the testing lab reports their test result. If a person is tested more than once on the same day, only one result is included. As the pandemic moves forward and it becomes more common for people to be tested multiple times, percent positive by test becomes a more useful metric for measuring COVID-19 activity in Wisconsin than percent positive by person. As the pandemic moves forward and it becomes more common for people to be tested multiple times, percent positive by test becomes a more useful metric for measuring COVID-19 activity in Wisconsin than percent positive by person.

The 7-day average percent positive (by test) trend line is an indicator for monitoring COVID-19 trends. Increasing trends in the 7-day average percent positive (by test) trend line could indicate an increase in COVID-19 infections.

The 7-day moving average of percent positive by test is calculated by taking the total number of positive tests from the past 7 days and dividing by the total number of all tests from the past 7 days. Using this numerator and denominator for the moving average (rather than the average of percent positive for each day) means that the moving average is responsive to the number of total tests conducted during that time. However, it may also lead this line to diverge somewhat from the daily percent positive line, especially if there are large differences between the number of tests processed on different days in this time period, or if the preliminary data are incomplete.

The percent positive by test data displayed above is similar to the statewide daily percent positive by test chart shown on the Wisconsin Summary webpage. However, while the data on the Wisconsin Summary page is updated daily, this data is only updated weekly, which may result in small differences between the data reported.

Data source: Wisconsin Electronic Disease Surveillance System (WEDSS).

About our data: How do we measure COVID-19-like Illnesses (CLI)?

How many emergency department (ED) visits are for COVID-19-like symptoms?

CLI visits are Wisconsin emergency department (ED) visits by Wisconsin residents with symptoms matching those of COVID-19. Data for Wisconsin residents visiting ED in other states are not available. This may result in under-estimates for some border communities with high numbers of residents served in other states.

Data source: Electronic Surveillance System for the Early Notification of Community-based Epidemics (ESSENCE).

CLI burden (CLI rate)

CLI burden (or CLI rate) is the total number ED visits with COVID-19-like illnesses per 100,000 Wisconsin residents.

CLI burden status Value (per 100,000 Wisconsin residents in the past two weeks)
Low CLI rate is less than or equal to 10.
Moderate CLI rate is greater than 10, but less than or equal to 50.
Moderately High CLI rate is greater than 50, but less than or equal to 100.
High CLI rate is greater than 100, but less than or equal to 350.
Very High CLI rate is greater than 350, but less than or equal to 1,000.
Critically High CLI rate is greater than 1,000.

 

CLI trajectory (percent CLI change)

CLI trajectory is the percent CLI change from the previous to the current week and indicates whether the change is statistically significant.

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

 

CLI activity level

CLI activity level is a summary indicator combining CLI burden and CLI trajectory. The CLI activity level is either low, medium, high, or very high.

CLI burden CLI trajectory CLI activity level
Low Shrinking Low
Low No Significant Change Low

 

CLI burden CLI trajectory CLI activity level
Low Growing Medium
Moderate Shrinking Medium
Moderate No Significant Change Medium
Moderately High Shrinking Medium

 

CLI burden CLI trajectory CLI 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

 

CLI burden CLI trajectory CLI activity level
Very High Shrinking Very High
Very High No Significant Change Very High
Very High Growing Very High

 

CLI burden CLI trajectory CLI activity level
Critically High Shrinking Critically High
Critically High No Significant Change Critically High
Critically High Growing Critically High

 

We plan to update our data each Wednesday by 5 p.m.

About our data: How do we measure Influenza-like Illnesses (ILI)?

How many Emergency Department (ED) visits are for Influenza-like symptoms?

ILI visits are Wisconsin ED visits by Wisconsin residents with symptoms matching those of influenza. Data for Wisconsin residents visiting EDs in other states are not available. This may result in under-estimates for some border communities with high numbers of residents served in other states.

A baseline normal range for ILI was determined using ILI activity of previous years. The normal range of ILI activity is calculated using data from past flue seasons (September through mid-April). The percent of ILI visits is categorized into low, moderate, or elevated activity as compared to the normal range. This follows the methodology of the ILI summary reports. The rolling 3-day averages are calculated over the two week period.

Data source: Electronic Surveillance System for the Early Notification of Community-based Epidemics (ESSENCE).

ILI activity Description
Low Rolling 3-day average is below the normal range.
Moderate Rolling 3-day average is within the normal range.
Elevated Rolling 3-day average is above the normal range.

 

We plan to update our data each Wednesday by 5 p.m.

 

How can I download DHS COVID-19 data?

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).

To download our data visit one of the following links:

You can find more instructions on how to download COVID-19 data or access archived spatial data by visiting our FAQ page. The data dictionary(PDF) provides more information about the different elements available in the data above.

Last Revised: November 24, 2020