Lyme disease is spread by the bite of an infected black-legged tick and is becoming more common in Wisconsin.
Public health professionals track Lyme disease in order to educate their communities and plan prevention efforts. View the video to the right to learn more about how we collect Lyme disease data.
The section below presents answers to frequently asked questions about Lyme disease and the data.
Frequently asked questions
Lyme disease is an infection caused by the bacterium Borrelia burgdorferi. The infection is spread by the bite of an infected black-legged tick (Ixodes scapularis), which are commonly called a deer tick. Symptoms can vary depending on the stage of infection and may include a characteristic bullseye rash, fever, arthritis, headache, fatigue, and facial paralysis. Lyme disease can be treated with antibiotics.¹ Lyme Disease Trends in Wisconsin, P-01295 (PDF) is a surveillance brief that offers more details on Lyme disease and its spread in Wisconsin.
The video below offers tips for preventing Lyme disease:
Tracking Lyme disease gives public health professionals a better understanding of how often Lyme disease happens in their county. With Environmental Public Health Tracking, we can monitor how many cases of Lyme disease occur in a county over time and can use that information to educate our communities and plan prevention efforts.
The source of the data is the Wisconsin Vectorborne Disease Program. Healthcare providers are required to report cases of Lyme disease. The Vectorborne Disease Program aggregates the cases and sends this information to Wisconsin Environmental Public Health Tracking Program.
- Cases of Lyme disease – The total number of Lyme disease cases in Wisconsin in a given year.
- Incidence of Lyme disease – The crude rate of new confirmed cases of Lyme disease in a given year, per 100,000 people. See our glossary entry on incidence rate for more information.
- Cases are based on the county of residence; some infections may have been acquired during travel to other areas.
- Data users should keep in mind that many factors contribute to illness. These factors should be considered when interpreting the data. Factors include:
- Socioeconomic status
- Demographics (age)
- Geography (rural, urban)
- Changes in the medical field (diagnosis patterns, reporting requirements)
- Individual behavior (outdoor hobbies)
- In 2008, the national surveillance case definition for Lyme disease introduced probable cases. In 2012, the Wisconsin Department of Health Services implemented a system to estimate cases of Lyme disease.
- Wisconsin Department of Health Services - Tickborne Infections
- Wisconsin Department of Health Services - Lyme Disease
- University of Wisconsin-Madison Department of Entomology - Tick Surveillance
- Lyme Disease Trends in Wisconsin (PDF)
- Wisconsin Climate and Health Program - Wisconsin Vectorborne Disease Toolkit (PDF)
- Centers for Disease Control and Prevention - Lyme Disease
Lyme disease data details
Total count of Lyme disease cases
These data are obtained from the Wisconsin Electronic Disease Surveillance System (WEDSS). WEDSS is a secure, web-based system used by public health staff, infection control practitioners, clinical laboratories, clinics, and other disease reporters to report communicable diseases. "Month" indicates the month of illness onset. County-level data are based on the county of residence of the case; some infections may have been acquired during travel to other areas. The entire state of Wisconsin is considered to be endemic for Lyme disease; thus, any Wisconsin resident is considered to be "exposed." "Confirmed cases" of Lyme disease include:
- Those with an erythema migrans (EM) rash that is greater or equal to 5 cm in diameter and diagnosed by a medical professional OR
- Those with at least one non-EM confirmatory sign or symptom indicating late manifestation of disease (arthritis, Bell's palsy or other cranial neuritis, encephalomyelitis, lymphocytic meningitis, radiculoneuropathy, or 2nd or 3rd degree atrioventricular block) that also has laboratory evidence of infection that meets criteria.
Non-confirmatory signs and symptoms include fever, sweats, chills, fatigue, neck pain, arthralgias, myalgias, fibromyalgia syndromes, cognitive impairment, headache, paresthesias, visual/auditory impairment, peripheral neuropathy, encephalopathy, palpitations, bradycardia, bundle branch block, myocarditis, or other rash. In 2008, the national surveillance case definition for Lyme disease introduced probable cases. Probable cases are any other physician-diagnosed Lyme disease cases with laboratory evidence of infection and non-confirmatory signs and symptoms. In 2012, to address the increased burden of Lyme disease reporting on local health departments and medical care providers, criteria in Wisconsin for reporting Lyme disease were revised so that only cases with an EM rash required public health follow up. Public health follow up involves a complete case investigation to collect information on other clinical signs and symptoms, possible exposures, and treatment. As an alternative to follow-up for every suspect Lyme disease case, a statistical method was implemented to estimate statewide cases based on the number of total laboratory reports for each year since 2012. The total state case count measure since 2012 is the sum of confirmed, probable, and estimated cases. However, the total state case count before 2012 and all total county case counts do not include estimated cases. For the total state case count, the data include only confirmed cases from 1991-2007; confirmed and probable cases from 2008-2011; and confirmed, probable, and estimated cases from 2012 to present. Note: In 2017, additional categories were introduced to allow for non-binary gender breakdowns of Lyme disease cases. Due to data limitations, it is likely that there is an underrepresentation of individuals in the non-binary gender categories.
Crude rates of confirmed cases per 100,000 population
These data are obtained from the Wisconsin Electronic Disease Surveillance System (WEDSS). WEDSS is a secure, web-based system used by public health staff, infection control practitioners, clinical laboratories, clinics, and other disease reporters to report communicable diseases. County-level data are based on the county of residence of the case; some infections may have been acquired during travel to other areas. The national surveillance case definition was revised in 2008 to include probable cases. In years prior to 2008, the incidence rate was calculated using confirmed cases as the numerator. Incidence rates after 2008 were calculated using confirmed and probable cases as the numerator. The incidence, or crude rate, is then calculated by dividing the numerator by the total number of people in the population of interest (for example, a county). Population estimates are derived from the U.S. Census. This is expressed as a number per unit population such as "per 100,000 population." Note: a crude rate does not take into account the differences in age distributions across counties and are therefore subject to bias. For example, as Lyme disease is less common among working age individuals, areas of the state with more working age individuals could appear, artificially, to have fewer cases generally. For more information on age-adjustment and biases see our glossary of terms.
Explore definitions and explanations of terminology found on the portal, like age-adjusted rate and confidence intervals.
Interested in environmental health data?
Join the environmental health listserv by sending an email to DHS Environmental Public Health Tracking with the subject line "Join envhealth listserv."