Many people worry about Lyme disease, but confusion about where it occurs and how clinicians diagnose it often leads to unnecessary concern, testing, and treatment, especially in the Pacific Northwest. Clear, evidence-based information helps patients understand their actual risk and avoid misdiagnosis.

Lyme disease develops when the bacterium Borrelia burgdorferi spreads through the bite of an infected black-legged tick, also known as the deer tick. Review of data published by the Harvard Medical School editorial advisory board member, Robert Shmerling, shows that these ticks live primarily in the Northeast, mid-Atlantic, and upper Midwest, where more than 90 percent of U.S. cases occur.

Lyme disease does not occur endemically in the Northwest, including Idaho and neighboring states. Instead, the Rocky Mountain wood tick and American dog tick carry other infections, including Rocky Mountain spotted fever, tularemia, and Colorado tick fever. According to CDC reports, Lyme disease diagnosed in patients who live in the Northwest almost always results from travel to endemic regions and not local exposure.

Lyme disease often develops early symptoms such as fever, headache, fatigue, with the hallmark rash, erythema migrans, an expanding red circular patch often referenced as having a “bull’s eye” appearance. When clinicians diagnose the condition early and treat it with antibiotics, most patients recover within a few weeks. If patients do not receive treatment, the infection can spread to the joints, heart, or nervous system, though this progression remains uncommon with appropriate care.

The term “Chronic Lyme Disease” creates significant confusion. Medical societies, including the CDC and multiple specialty organizations, do not recognize “Chronic Lyme Disease” as a valid diagnosis. Research has not shown evidence that persistent infection causes ongoing symptoms after appropriate treatment. Studies also demonstrate that prolonged or repeated antibiotic therapy does not improve outcomes and can cause harm.

Post-Treatment Lyme Disease Syndrome (PTLDS) describes patients who continue to experience symptoms after completing standard therapy. According to CDC, 5 percent to 10 percent of patients report persistent fatigue, pain, or cognitive symptoms after treatment. Researchers have not found evidence that PTLDS results from ongoing infection. Additional antibiotics do not improve these symptoms.

Current guidelines from the Infectious Diseases Society of America, American Academy of Neurology, and American College of Rheumatology define PTLDS using specific criteria: (1)

the patient had a documented episode of Lyme disease and received recommended antibiotic treatment; (2) objective signs of infection resolved or stabilized after treatment; (3) the patient developed symptoms such as fatigue, musculoskeletal pain, or cognitive difficulty within six months of diagnosis; (4) these symptoms persisted for at least six months after treatment; (5) no evidence suggests active infection or another condition that better explains the symptoms.

Despite these updates in guidelines, misdiagnosis remains common. Clinicians evaluating patients for Lyme disease often find other conditions, including arthritis, autoimmune disease, or neurologic disorders. For individuals in the Northwest, the key point remains clear: Lyme disease is rare and typically linked to travel, while other tick-borne illnesses occur more commonly in the region.

The best way to prevent tick-borne illness is to avoid tick bites. Ticks are most active from April through September and commonly live in grassy, brushy, or wooded areas. Staying on trails while hiking decreases opportunities for tick contact. The CDC reports that showering within two hours of being outdoors may reduce the risk of tick-borne disease. Before backpacking or camping, treat clothing and gear with products containing 0.5 percent permethrin, which can remain protective through several washings. Use EPA-registered insect repellents such as DEET, picaridin, IR3535, oil of lemon eucalyptus (OLE), or PMD. OLE and PMD should not be used on children younger than 3. Insect repellent should be applied after sunscreen.