What The COVID-19 Pandemic Looks Like In Wisconsin: Maps And Charts
Editor's note: This article was originally published on April 1, 2020 and has since been updated, with the most recent changes made on Feb. 11, 2021. Data visualizations are updated once daily as new numbers become available.
Understanding when and where COVID-19 is spreading around Wisconsin is a matter of constantly moving targets. Tracking data related to the pandemic can help clarify this torrent of information. Click on the table of contents or swipe the page to view a series of visualizations that depict the impacts of COVID-19 across the state.
Knowing the trajectory of the outbreak in Wisconsin can help public health officials discern to what degree actions designed to slow its spread are working. It can also help healthcare workers and hospital systems better prepare for surges in patients.
More information about COVID-19 and how it is affecting the state can be found in a WisContext FAQ that provides explanations to common questions about the disease and in coverage by PBS Wisconsin and Wisconsin Public Radio.
Statewide cases and deaths
Key pieces of information include the number of new infections and deaths reported on a daily basis. If the number of new infections reported rises day to day, that's a sign that the outbreak is growing quickly. Increasing daily deaths is a lagging indicator that reflects a preceding rise in cases.
The goal of public health officials is for the number of newly reported cases and deaths to fall over time. Since the period between coronavirus exposure and the onset of symptoms can be up to two weeks, and death in serious cases can follow long after infection, any discernible effects of public health measures are delayed.
A simple way to understand the short-term dynamics of an outbreak is to track a 7-day moving average of newly confirmed cases and deaths. The trend line of these moving averages is sensitive to fluctuating daily numbers, and can help indicate when an outbreak is surging, has peaked or is declining.
The total number of people in Wisconsin who have tested positive for COVID-19 and those who have died as a result help provide a longer-term picture of the state's outcomes. If cases and deaths are growing rapidly by the day, the pace of total infections and fatalities over time will have steep upward trajectories, while decreases in daily numbers leads to a flatter pace.
Another relevant COVID-19 metric is the case fatality rate. This measure reflects the percentage of confirmed cases that have resulted in death. However, it doesn't reflect the outcomes of unconfirmed COVID-19 cases, and is therefore likely higher by an unspecified degree than the disease's actual death rate.
County cases and deaths
The number of confirmed COVID-19 cases and deaths varies widely among Wisconsin's 72 counties. Tracking the daily number of cases and deaths at the county level reveals more localized trends in the pandemic, with surges growing at different times in different places.
As the pandemic continues over time, the daily case and death counts at the county level can result in broader regional patterns of where COVID-19 has spread widely, where it is not as prevalent and where its deadly effects are most acute. A county-level map of total infections and deaths can help shine light on these important geographic differences.
County-level statistics about local COVID-19 outcomes are more informative when considered in terms of the size of a local population. Ten infections in a large, densely populated metro area with multiple hospitals is much different than 10 infections in a tiny community without a health clinic. It's therefore useful to evaluate local outbreaks relative to the size of local populations, commonly known as a per capita rate — in this case, cases or deaths per 100,000 residents.
County-level trends in COVID-19 transmission around Wisconsin can also be observed over time and through different types of groupings. Adjusting case rates to population size can provide further insight about the relative severity of outbreaks. In this case, visualizing the growth in case rates over the course of the pandemic through a county's population sizes shows how COVID-19 shifted between different parts of the state as successive waves of infections were reported.
The shorter-term dynamics of COVID-19 transmission in Wisconsin reflect the status of the pandemic at any given moment in time, and are examined through counting the total number of confirmed cases over recent time periods. Plotting the number of cases reported statewide and within each county over the most recent 14-day and 30-day periods can help estimate a rough number of people who may currently be experiencing symptoms of COVID-19 and who are possibly infectious.
Another way to visualize recent confirmed COVID-19 cases across Wisconsin is to depict the per capita rates of confirmed cases in each county, with those over the previous 14 and 30 days depicting where outbreaks are currently spreading.
Public health officials have worked to expand COVID-19 testing capacity in Wisconsin in order to provide a more complete picture of the number of people infected with the disease. The total number of confirmed infections in Wisconsin is likely considerably smaller than the true number of infections. Many people who are infected may not show symptoms, and others with mild or moderate symptoms may not be tested due to testing availability. Still, understanding how many tests indicate infections can provide a snapshot of the disease's prevalence.
A metric related to these efforts is the percent of tests that come back with positive results, which is known as a test-positivity rate. While the rate is subject to daily fluctuations, its longer-term trajectory can reveal the severity of Wisconsin's outbreak. Higher rates can indicate that testing strategies are missing many sick individuals, while a declining rate over time could indicate the state’s outbreak is coming more under control.
There are multiple ways to calculate test-positivity rates. One common method is to divide the number of people who test positive by the number of people who are tested. Another method is to divide all positive tests by the total number of tests with results. The rates based on these two methods may diverge over time as a growing number of people receive repeat tests. Additionally, the number of tests performed each day is highly variable, which can lead to daily fluctuations in positivity rates. To better understand trends in positivity, rates are calculated based on moving 7-day periods.
Throughout much of the pandemic, the Wisconsin Department of Health Services calculated test-positivity by both tests and people. In February 2021, the agency dropped its calculations by people, citing a shrinking number of Wisconsinites who had never been tested. For comparison, an archived chart of the 7-day test-positivity average by people running from March 9, 2020 through Feb. 6, 2021 shows how this method of calculation can result in different daily figures. However, the different methods show parallel trends in test-positivity over time.
Before presenting these test-positivity calculations, WisContext calculated daily positivity rates and 7-day averages using data differently. In this case, the rates were based on test results on the day they were reported, rather than the subsequent method where rates reflected the date of the test result. Due to reporting lags, that previous method resulted in slightly different positivity rates, and WisContext ended its tracking of positivity with this method after Sept. 29, 2020 to align with the state health department's methods.
Tracking the test-positivity rate at a more local level is important for local policymaking related to public health guidelines for schools and group gatherings, with one common benchmark calling for fewer than 5% of test results coming back positive. Due to often wide differences in the number of tests reported per day at a local level, particularly in places with smaller populations, the 7-day and 14-day averages of the test-positivity rate provide a more reliable figure for public health officials to monitor.
If public health measures that are designed to slow the spread of COVID-19 have an effect, and the number of new cases begins to fall, a plot of total infections over time would become less steep, or flatten. It's the origin of the ubiquitous term "flattening the curve" in discussions about COVID-19.
Flattening the curve is primarily aimed at protecting the capacity of healthcare systems to treat serious cases of COVID-19 while maintaining other essential care. A relatively small but significant number of cases are serious enough to warrant hospitalization, with the most serious requiring intensive care. The daily number of new hospitalizations due to COVID-19 and the 7-day running average of this figure show how the need for this resource fluctuates.
The daily number of new hospitalizations statewide due to COVID-19 doesn't show the breadth of the disease's impact on Wisconsin's hospitals because it doesn't include the number of discharges or regional differences. Instead, the total daily number of COVID-19 patients in the state's seven healthcare emergency readiness regions — coalitions of hospital networks that coordinate resources — is a metric healthcare and public health officials in the state track closely to gauge their capacity to address the pandemic.
As is the case across the United States, Wisconsin is seeing demographic disparities in the number and severity of COVID-19 cases, as well as in COVID-19-related deaths. One of the primary risk factors is increasing age, which is evident from the statewide data on the numbers of cases, hospitalizations and deaths from COVID-19.
Reflecting national patterns, Wisconsin is reporting disparities in COVID-19 cases, hospitalizations and deaths based on racial and ethnic classifications. Data show that some groups, including Indigenous, Black and Hispanic Wisconsinites, are diagnosed with COVID-19 at higher rates than white Wisconsinites. Indigenous and Black Wisconsinites are also being hospitalized and dying at higher rates.
Wisconsin regularly receives allocations of COVID-19 vaccine doses from the federal government, with the number provided to states and territories based on population and supplies available from manufacturers. Healthcare systems, pharmacies and other vaccine providers in the state make requests for doses, and the Wisconsin Department of Health Services factors those requests into its weekly requests to the U.S. Department of Health and Human Services.
The administration of COVID-19 vaccines to Wisconsin residents is not an immediate process, nor is it geographically uniform. Vaccination is authorized for individuals ages 16 and older, which represents roughly 80% of the state's total population of more than 5.8 million people.
COVID-19 vaccines produced by Pfizer and Moderna require two doses that are administered several weeks apart. The state therefore tracks not only the daily number of doses but likewise the total number of people in Wisconsin who have completed their vaccine series, statewide and at the county level. Scientists have estimated that upward of 70% of the population needs to be vaccinated to effectively limit the spread of the coronavirus and halt the pandemic. Wisconsin officials set a target of fall 2021 for this goal.