What The COVID-19 Pandemic Looks Like In Wisconsin: Maps And Charts
Editor's note: This article was originally published on April 1 and has since been updated, with the most recent changes made on July 10. Data visualizations are updated once daily as new numbers become available.
The COVID-19 pandemic is sweeping across Wisconsin. The outbreak is having major ramifications for public health and hospital systems, which in turn affects the ongoing spread of the disease.
Understanding where, when and how rapidly COVID-19 arises around Wisconsin — and how badly its effects are felt — is a matter of constantly moving targets. It can be difficult to keep up with and make sense of the information related to COVID-19 infections and fatalities being shared by state and local health departments on a daily basis.
Tracking data related to the pandemic can help clarify this torrent of information. Here are several visualizations that depict the impacts of COVID-19 across Wisconsin.
First, 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.
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 rapidly day-to-day, that's a potentially worrying sign that the outbreak is growing quickly and threatening hospital capacity. A rise in daily deaths would also be a negative indicator.
The goal of public health officials is to see the number of newly reported cases and deaths fall over time. Because the time between exposure and the onset of symptoms can be up to two weeks in the case of COVID-19, and death in serious cases can follow long after infection, any discernible effect of public health measures would be delayed.
A related and similarly important element is the total number of people who have been infected and have died. If cases and deaths are growing rapidly by the day, plots of total infections and fatalities over time would show that plainly with a steep upward trajectory.
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. Hence the ubiquitous term "flattening the curve." in discussions about COVID-19.
A common way to visualize the dynamics of an outbreak and potential effects of strategies designed to slow its transmission is to track a 7-day moving average of newly confirmed cases and deaths. The trend line of these moving averages is more sensitive to fluctuating daily numbers, and can help indicate when the outbreak has peaked, or is declining or surging.
The total number of confirmed infections in Wisconsin is likely much smaller than the true number of infections. Many people who are infected may not show symptoms, and others with mild or moderate symptoms are unlikely to be tested due to limited test availability and shortages of testing supplies. Still, understanding how many people diagnosed with COVID-19 out of the total number who are tested can provide a snapshot, however incomplete, of the disease's prevalence in relation to other commonly circulating respiratory diseases with similar symptoms, such as influenza.
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.
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. A higher rate can indicate that testing strategies are missing many sick individuals. Instead, officials want to see the rate go down over time, which could indicate the state's outbreak is coming under control.
A more complex 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 higher than the disease's actual death rate.
The total numbers of new infections and tests over time is only so useful for a geographic area as large as Wisconsin. The most acute health effects of COVID-19 are being experienced at a local level.
The number of confirmed cases and deaths related to the disease varies widely among Wisconsin's 72 counties. At least one resident of each has been diagnosed with COVID-19, but the total number of cases runs into the thousands in multiple counties. Similarly, most deaths are concentrated in a handful of counties. Tracking the daily number of cases and deaths by county reveals more localized trends in the pandemic, with outbreaks experienced at different times in different places.
As the pandemic continues over time, the day-to-day case and death counts at the county level result in broad regional patterns of where COVID-19 has spread widely, where it is not as prevalent and where its deadly effects are most severe. A county-level map of total infections and deaths can help shine light on these important geographic differences.
Looking at county-level data could be deceiving without some knowledge of a local outbreak's magnitude compared to the size of a local population. Ten infections in a large, densely populated metro area with multiple hospitals is a world apart from 10 infections in a tiny community without a single health clinic.
That's why it is useful to evaluate local outbreaks relative to the size of local populations. This is commonly known as a per capita rate — in this case, cases or deaths are adjusted to per 100,000 residents.
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 a series assembling Wisconsin Public Media reporting about the crisis, as well as in coverage by PBS Wisconsin and Wisconsin Public Radio.