How We Track Respiratory Viruses in Dane County

If you follow us on social media or go to our website, you’re probably familiar with the work we do to track COVID cases. (If you’re not, check out our data and dashboard page.) But did you know we also keep an eye on other respiratory viruses, like the flu and RSV? We use a few different data sources to keep track of what’s happening in Dane County and Wisconsin-- and you can use some of them too!

Monitoring disease reports

With some diseases, like COVID, positive test results are required to be reported to our state public health disease database (WEDSS). We use these data to track trends over time, ensure treatment for people who test positive, and follow up with people who were possibly exposed. This helps us prevent outbreaks of serious diseases. You can find a full list of reportable diseases on the DHS website.

COVID-19 is a reportable disease since it is so new, but other respiratory diseases like RSV are not because they are common in our area. Influenza is only reportable if someone is hospitalized, if someone under 18 dies from the flu, or if there’s an unusual strain found. So we aren’t able to track case trends from these data, but they are useful for tracking severe outcomes from the flu in Dane County.

Department of Health Services

Source: Wisconsin Respiratory Virus Surveillance Report, January 7, 2023
 

The Wisconsin state health department puts out weekly respiratory reports during flu season (fall-spring). These reports pull from several different data sources. One is ILINet, a CDC database. ILINet collects data from a sample of outpatient clinics, who tell CDC the number of people with influenza-like illness (ILI) that they see in their offices. ILI is when a patient has a fever of 100 degrees or higher, and either a cough or sore throat. This helps us track general trends of respiratory illnesses to give us a complete picture of what’s happening.

Other data come from 40 different laboratories in Wisconsin who test for different respiratory viruses. DHS uses the percent of tests that are positive to compare viruses to each other. This lets us see the overall Wisconsin trend for the flu, RSV, and other respiratory viruses (like parainfluenza).

The downside to these data is that they’re not specific to Dane County, so we don’t know what’s happening on the county level. But the DHS respiratory reports also provide regional data for influenza-like illness, so we can see what is happening in the southern region of Wisconsin. The Southern region has shown a similar ILI trend as the state so far this season, although statewide ILI levels are back down to low, while the Southern region is still at a moderate level.

Wisconsin State Lab of Hygiene

The Wisconsin State Lab of Hygiene (WSLH) is Wisconsin’s public health laboratory, and is part of UW-Madison. They test samples from health care facilities and report data on their website. The data overlap a lot with the DHS Weekly Respiratory Reports, but it is another place to find regional and state data. The state lab pulls out RSV activity and influenza activity separately.

Putting it all together

We keep ourselves informed on the latest respiratory trends through an internal one page summary. We look at all of the data sources listed above and highlight if the overall trend is increasing, decreasing, or plateauing. It’s a basic way to be a little more informed on what’s happening in our area. When there are notable trends, we share them on social media for the general public.

What’s next?

Given the importance of respiratory viruses over the past couple of years, we think it’s important to continue monitoring trends. We are investigating how to get more data at the local level to share with the public. Until then, we encourage anyone who is interested to check out the regional, state, and national resources we’ve linked to in this blog.