Respiratory Virus Data
This page is a summary snapshot of the latest information on viral respiratory illness in Wisconsin. It shows the respiratory illness activity level and trajectory for the previous week and provides key findings regarding respiratory virus transmission in Wisconsin.
What to know
- Statewide respiratory illness levels are low.
- COVID-19, influenza, and RSV activity levels are minimal based on emergency department data, and laboratory testing. Wastewater data also shows little activity for these viruses.
- Rhinovirus/enterovirus and parainfluenza virus detections in laboratory data are elevated.
- DHS recommends seasonal vaccines for flu, COVID-19, and RSV. To find more information about respiratory vaccines, visit the Wisconsin Immunization Program.
What you can do
Even when respiratory illness levels are very low or low, it is important to keep up with prevention strategies. Follow these tips to help keep you and your loved ones healthy:
- Stay home if you are sick.
- Cover coughs and sneezes.
- Stay up-to-date with vaccines.
- Take steps for cleaner air, such as gathering outside, opening windows or doors, or using a high-efficiency particulate air (HEPA) cleaner.
- Wash your hands and practice good hygiene.
Additional precautions, such as wearing a mask and physical distancing, should be considered when illness levels are moderate or high or very high. If you or people around you have risk factors for severe illness, consider additional precautions at any time.
Data shown are subject to change and will be updated as more information is available.
How to use the data visualizations
Emergency department data
The first visual on this page provides the respiratory illness levels and trajectories for emergency department visits associated with overall respiratory illness, COVID-19, influenza, and RSV for the most recent week of data.
The line graph shows the percent of all emergency department (ED) visits with a diagnosis of a respiratory illness by week. Users can hover over the trend line on the graph to see more detailed information.
The emergency department levels and trajectories can be filtered to show data for one of the five Wisconsin public health regions by using the dropdown menu.
Laboratory testing data
The second half of the visual provides information on respiratory virus laboratory testing completed in clinical laboratories. It displays the five viruses with the highest percent positivity, from the list of viruses displayed. The virus with the highest percent positivity is listed as number 1. The arrows next to the virus’ name indicate whether the percent positivity for each of these viruses is increasing, decreasing, or is stable.
Technical data notes and data sources
Emergency department data
Data source: ESSENCE (Electronic Surveillance System for Early Notification of Community Based Epidemics) from the National Syndromic Surveillance Program.
Approximately 95% of non-federal Wisconsin emergency departments (EDs) are represented in the dataset, and most EDs transmit visit information into ESSENCE within 24 hours.
Calculation of percent of ED visits by diagnosis: Overall respiratory illness activity trends over time are calculated using ED visits meeting the CDC (Centers for Disease Control and Prevention) Broad Acute Respiratory Discharge Diagnoses (DD v1), which measures acute respiratory infection (ARI). This measure uses diagnoses for viral illnesses such as COVID-19, influenza, and RSV, in addition to general respiratory illnesses, such as cough or sore throat to measure the overall respiratory illness in the community.
Weekly proportion of ED visits for respiratory illness is calculated by dividing the number of visits to the ED with a diagnosis meeting the CDC Broad Acute Respiratory DDv1 definition from Sunday through Saturday by the total number of visits to the ED for the same time period.
Calculation of ED activity level metric: Activity level metrics for overall respiratory illness, COVID-19, influenza, or RSV categorize the current amount of visits to the ED for each of these conditions compared to the number of visits during times of the year when these viruses are circulating at their lowest level in the community. Activity levels for the 2024–2025 respiratory season are calculated using ED visits meeting the following ESSENCE diagnosis categories:
- Overall respiratory illness: CDC Broad Acute Respiratory DDv1
- COVID-19: CDC COVID-Specific DDv1
- Influenza: CDC Influenza DD v1
- RSV: CDC Respiratory Syncytial Virus DDv1
Activity levels are provided by CDC. To view the detailed methodology used to calculate these values, see the CDC data notes describing these calculations.
| Level | Percent of weekly ED visits for overall respiratory illness | Percent of weekly ED visits for COVID-19 | Percent of weekly ED visits for influenza | Percent of weekly ED visits for RSV |
|---|---|---|---|---|
| Very Low | 0% to <10.6% | 0% to <0.5% | 0% to <0.1% | 0% to <0.05% |
| Low | 10.6% to <14.4% | 0.5% to <1.4% | 0.1% to <1.8% | 0.05% to <0.4% |
| Moderate | 14.4% to <18.2% | 1.4% to <2.3% | 1.8% to <3.4% | 0.4% to <0.8% |
| High | 18.2% to <22.0% | 2.3% to <3.3% | 3.4% to <5.0% | 0.8% to <1.2% |
| Very High | 22.0% or above | 3.3% or above | 5.0% or above | 1.2% or above |
Calculation of ED trajectories: The weekly respiratory illness trajectory for each diagnosis is the measure of change in the proportion of ED visits from the previous week to the next week. There are two ways for the trajectory to be increasing or decreasing.
- The percent change of the proportion of ED visits from the previous week to the current week must be over the minimum threshold, which is 10% for COVID-19, influenza, and RSV and at least 5% for overall respiratory illness, or
- The percent change must be consistently higher or lower for three consecutive weeks, and the percent change from the first week to third week must be at least 10% for COVID-19, influenza, and RSV, and at least 5% for overall respiratory illness.
Laboratory testing data
Data source: National Respiratory and Enteric Virus Surveillance System (NREVSS).
NREVSS is a sentinel network of laboratories located through the U.S., including clinical, public health, and commercial laboratories. Participating U.S. laboratories voluntarily submit reports to CDC NREVSS detailing the total number of aggregate tests performed each week to detect select respiratory and enteric viruses, as well as the number of positive tests that week. These diagnostic tests are limited to nucleic acid amplification tests (NAATs) or polymerase chain reaction (PCR) tests.
Calculation of percent positivity: The percent of tests positive is calculated by dividing the number of positive tests (for each virus) by the total number of tests administered (for that virus), then multiplying by 100% [(# of positive tests/total tests) x 100%]. The three-week moving average of percent positivity is shown in these charts.
Calculation of laboratory trajectories: The virus-specific trajectory based on laboratory testing is a measure of change in the proportion of laboratory tests positive from the previous week to the next week. There are two ways for the laboratory trajectory to be increasing or decreasing.
- The percent change of the percent positivity from the previous week to the current week must be over the minimum threshold, which is 10%, or,
- The percent change must be consistently higher or lower for three consecutive weeks, and the percent change from the first week to third week must be at least 10%.
Additional resources
Learn more about the CDC calculated levels.