• Lyme disease is the most common tickborne infection in Chicago, caused by the bacterium Borrelia burgdorferi and rarely, Borrelia mayonii.
  • Lyme is transmitted to humans through the bite of black-legged ticks (also known as deer ticks in the eastern United States) and western black-legged ticks in western United States infected with the bacterium Borrelia (Figure 1). 
  • Approximately 20 % of infected patients recall tick bites.
  • Infection occurs at least 36 - 48 hours after tick attachment. 
  • The incubation period is 3-30 days after the tick bite.
  • The primary reservoir and host for the bacteria: Small rodents, including the white-footed mouse (Figure 2).
  • Host for ticks: Whitetail deer (Figure 3).
Figure 1: Common Ticks Associated with Lyme Disease in North America.
Two hard-bodied ticks that carry the spirochetes that cause Lyme disease are shown, along with representations indicating their size during the developmental stages.  Tickborne Diseases — Confronting a Growing Threat | NEJM


Figure 2: White footed mouse

Figure 3: Whitetail deer


Clinical Picture

Lyme disease has three stages, each with different clinical manifestations. Without appropriate antibiotic treatment, disease can progress from stage 1 to stage 2 or 3 within weeks or months.
  • Stage 1 occurs 3 to 30 days after a tick bite and usually consists of Erythema Migrans (EM), a slowly expanding skin lesion, accompanied by flulike symptoms (fever, headache, tiredness, swollen lymph nodes, and joint and muscle pain). EM occurs in 70-80% of infected people and typically, but not always, appears like a bull’s eye or target appearance (Figure 4). 
  • Stage 2 (or early dissemination infection stage) occurs weeks later. In this stage the manifestations may include multiple EM rashes distant from the site of tick bite (Figure 5) and neurologic symptoms including aseptic meningitis (typically with a lymphocytic pleocytosis), cranial neuritis (including Bell’s Palsy), or encephalitis. Another early disseminated form of disease is Lyme carditis which may include second-degree and third-degree heart blocks or myopericarditis
  • Stage 3 (late dissemination infection stage) usually occurs months after a tick bite. This stage is commonly associated with intermittent or persistent arthritis in one or a few joints, most commonly the knees, over a period of several years.
Figure 4: Erythema Migrans


Figure 5: Multiple Erythema Migrans (Early Lyme disease dissemination)


Laboratory Diagnosis

  • When assessing a patient for Lyme disease, healthcare providers should consider:
    • The signs and symptoms of Lyme disease
    • The likelihood that the patient has been exposed to infected blacklegged ticks.
    • The possibility that other illnesses may cause similar symptoms.
    • Results of laboratory tests, when indicated.
  • CDC currently recommends a two-step testing process for Lyme disease. Both steps are required and can be performed on the same blood sample. Serologic testing should use validated first- and second tier tests (Figure 6):
    • Standard two-tier test (STTT): An initial (first tier) positive or equivocal enzyme immunoassay (EIA) or immunofluorescent assay (IFA) followed by a second positive Immunoglobulin M (IgM) or Immunoglobulin G (IgG) western immunoblot (WB).
    • Modified two-tier test (MTTT): An initial (first tier) positive or equivocal enzyme immunoassay (EIA) or immunofluorescent assay (IFA) followed by a second positive IgM or IgG enzyme immunoassay (EIA).
    • If the first step in testing is negative, no further testing is recommended. 
    • If the first step is positive or equivocal/indeterminate, the second step should be performed.
    • The overall result is positive only when the first test is positive or equivocal and the second test is positive.
  • Other methods for diagnosis:
    • Culture for B. burgdorferi or B. mayonii
    • PCR for B. burgdorferi or B. mayonii
    • Immunohistochemical assay (IHC)
  • Key points to remember:
    • Most Lyme disease tests are designed to detect antibodies made by the body in response to infection.
    • Antibodies can take several weeks to develop, so patients may test negative if infected only recently.
    • Antibodies normally persist in the blood for months or even years after the infection is gone; therefore, the test cannot be used to determine a cure.
    • Infection with other diseases, including some tickborne diseases, or some viral, bacterial, or autoimmune diseases, can result in false positive test results.
    • Some tests give results for two types of antibodies, IgM and IgG.  Positive IgM results should be disregarded if the patient has been ill for more than 30 days.

Figure 6:

Figure 6. Standard 2-tier and modified 2-tier algorithms for serodiagnosis of Lyme disease. The US Centers for Disease Control and Prevention recommended a standard 2-tier algorithm (A) and the modified 2-tier algorithm (B).
*For patients with signs or symptoms consistent with Lyme disease for less than 30 days, the provider may treat and follow up with a convalescent- phase serum sample. Patients with erythema migrans should receive treatment of the bases of clinical diagnosis. WB: Western blot. (2)


Disease Prevention

Steps to prevent Lyme disease include using insect repellent, checking the body after being outdoors (figure 7), removing ticks promptly, applying pesticides, and reducing tick habitat.

Figure 7: Preventing Lyme disease by checking the body after being outdoors. (CDC)

How to remove ticks:


  1. Data Finder - Health, United States (cdc.gov)
  2. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 27, No. 8, August 2021.
  3. N Engl J Med 2018; 379:701-703 DOI: 10.1056/NEJMp1807870.
  4. https://emedicine.medscape.com/article/330178-clinical?form=fpf 
  5. https://www.cdc.gov/lyme/treatment/lymecarditis.html
  6. Mandell, 2020, Principles and Practice of Infectious Diseases, ELSEVIER.
  7. https://www.pcds.org.uk/clinical-guidance/lyme-disease
  8. Treatment of Lyme Disease | Lyme Disease | CDC
  9. Clinical Infectious Diseases, Volume 72, Issue 1, 1 January 2021, Pages e1–e48, https://doi.org/10.1093/cid/ciaa1215

Lyme disease Reporting

For Clinical Questions Contact:
The CDPH Disease Reporting Hotline at 312-743-9000

*After hours, weekends, and holidays, call 311 and ask for the communicable disease physician on-call (or 312-744-5000 if outside the City of Chicago)

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