Lyme disease is a bacterial infection transmitted to humans through the bite of an infected tick. Caused by the bacterium Borrelia burgdorferi, it can affect multiple body systems if not treated early. Lyme disease is now considered endemic in Illinois, meaning the state has established populations of the vector and sees recurring human cases. Awareness of this risk is important as the tick population and the bacteria’s geographic spread continue to expand.
Current Prevalence and Case Trends in Illinois
Lyme disease incidence in Illinois has shown an upward trend over the last decade, indicating a rising risk for residents across the state. The number of reported cases has steadily increased, with over 1,700 confirmed and probable cases documented between 2018 and 2022 alone. This increase reflects the growing presence of the disease-carrying tick population in the state.
Illinois’s case rate remains at a higher level than many non-endemic areas of the country. For example, the rate of confirmed cases per 100,000 people reached 4.3 in 2021, a jump from the 1.1 rate reported in 2010. This rate provides context when comparing Illinois to states outside the primary endemic zone, such as Alabama, which typically sees rates below one case per 100,000 people.
Surveillance data collected by the Illinois Department of Public Health (IDPH) and the Centers for Disease Control and Prevention (CDC) only represents confirmed and probable cases. The true number of infections is likely much higher, as many cases go undiagnosed or are not reported to public health authorities. This suggests that the risk of exposure in Illinois is greater than the official statistics indicate.
Identifying the Vector and High-Risk Areas
Lyme disease is transmitted exclusively by the blacklegged tick, Ixodes scapularis. This species is the only one in Illinois known to transmit the Borrelia burgdorferi bacteria to humans. The highest risk of transmission occurs during the nymph and adult life stages. Ticks are most active from early spring through late fall, though adults may be active any time temperatures are above freezing.
The preferred environment for the blacklegged tick is wooded, brushy areas, especially those with dense leaf litter that provides the moisture and shade necessary for survival. The highest concentration of these ticks is found in the northern and central regions of the state. Specific areas, including counties in the northeastern and central parts of Illinois, have been identified as high-risk zones, such as Macon, Piatt, and Kane counties.
These high-risk areas typically contain mesic, upland, oak-hickory forests that offer the ideal habitat for the tick and its hosts, like white-footed mice and deer. As the tick’s range expands, the risk of encountering an infected tick is no longer confined to the far northern counties but is a consideration across much of the state. The presence of the bacteria has been confirmed in ticks collected from 47 counties as of 2024, showing the broad geographic reach of the threat.
Localized Prevention Measures
Illinois residents can reduce their risk of Lyme disease exposure by taking specific measures when spending time outdoors. Since ticks thrive in vegetation, staying on marked trails and avoiding walking through tall grass and dense brush when hiking is advised.
Personal Protection
Treating clothing and outdoor gear with products containing Permethrin provides long-lasting protection against ticks. For skin protection, use an Environmental Protection Agency (EPA)-registered repellent that contains DEET, picaridin, or oil of lemon eucalyptus. After coming indoors, remove clothing and immediately place it in a dryer on high heat for at least ten minutes to kill any clinging ticks. Promptly showering after outdoor activity can also help wash off unattached ticks.
Tick Checks and Removal
The most effective protective measure is performing a thorough tick check on yourself, children, and pets after any time spent in a high-risk habitat. Ticks prefer to attach to hard-to-see areas, such as the scalp, in and around the ears, under the arms, and between the legs. If a tick is found attached, remove it gently using fine-tipped tweezers, pulling upward with steady, even pressure.
If a tick bite occurs, monitor the site closely for several weeks following removal. Watch for a rash or the onset of flu-like symptoms, such as fever, chills, and muscle aches, which can signal an infection. Early detection and treatment with antibiotics prevent the progression of Lyme disease to more serious complications.