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confirmed & probable cases


The goal of this COVID-19 mapping project is to put COVID in its spatial and social context, to allow better exploration and understanding of geographic patterning in detected cases and deaths. We will also explore how the distribution of COVID-19 cases change with respect to social risk factors, such as urban/rural environment, age and race. We have developed this interactive map for you to physically explore the spread of COVID-19 cases around the state of Michigan through space and time, from the first detected case on until . To see how COVID-19 cases change over time with social distancing policies, visit our Timeline page.

How is COVID-19 transmitted?

Close contact. Surfaces. Respiratory droplets.

COVID-19 is transmitted through respiratory droplets. Respiratory droplets, according to the WHO, refers to droplets > 5-10 μm (micrometers) in diameter. Transmission by respiratory droplets typically requires close contact between individuals. The WHO defines such contact as within about 1 meter (approximately 3 feet) of someone experiencing respiratory symptoms like coughing or sneezing. Transmission can also occur through droplets on surfaces, and the WHO has updated its guidance on COVID-19 transmission to account for emerging studies that suggest that airborne transmission of the virus through aerosolized (smaller) droplets may be possible in certain circumstances.

Where are we getting these numbers?

These data come from the Michigan Department of Health and Human Services and reflect counts of confirmed (and probable) COVID-19 cases in Michigan including cases reported from the Michigan Department of Corrections (MDOC). As a result, this specifically reflects risk among those who are being tested in the state of Michigan. Information on testing in Michigan is available at the coronavirus page. However, it is important to keep in mind that the numbers on the map here reflect not the total number of COVID-19 infections, but confirmed cases who are being tested. Specific criteria are required in order to be tested, and this has changed over time. The percent positive rate is a good way to contextualize how many of the ‘true’ cases are being captured. The cumulative percent positive rate is about 25% in the state of Michigan, meaning that on average, for every case detected by a COVID-19 test, there are three negative tests. This high rate of positives indicates we are likely missing a good portion of the true extent of cases, indicating that risk estimates on this map are conservative.

What can we learn from mapping COVID-19?

Importance of social distancing

This droplet-based transmission is why wearing masks, washing your hands carefully, and maintaining 6 feet of distance whenever possible can help to stem the spread of coronavirus. Additionally, droplet transmission indicates that individuals need to be close to one another in physical space to spread the virus. This means that someone’s risk of infection is strongly influenced by local rates of infection in their surroundings, making a map of local disease incidence potentially helpful for understanding infection risks in your area.

Locating risk areas

However, we have learned that exposure to the SARS-CoV-2 virus is not the only factor driving transmission in Michigan and other U.S. states. For example, areas with more elderly individuals may be at higher risk of having cases of severe disease and death. Places with higher rates of poverty, unstable housing, and pre-existing medical conditions have also seen increased risk.

Estimating infection

Finally, our map currently includes only reported cases, and necessarily represents an underestimate of the amount of infection that has and continues to occur. This is due to the fact that many cases may be fully asymptomatic, and that some individuals with mild symptoms of COVID-19 may not seek medical attention. These effects may vary in space, and these maps should be viewed with these limitations in mind.

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