Can Borrelia-specific IgM persist without indicating active infection?

Borrelia-specific IgM is best understood as an early, imperfect marker of exposure-associated immune activation—not as a standalone indicator of viable, current infection.

Clinical evidence

• IgM generally precedes IgG in Lyme borreliosis. In patients with erythema migrans, Borrelia-specific IgM commonly becomes detectable about 2–4 weeks after symptom onset and peaks around 6–8 weeks.
• Serology can still be negative early in illness, including during the first 4–6 weeks; prompt antibiotic treatment may also blunt or prevent measurable seroconversion.
• IgM may persist despite clinical recovery and treatment. Longitudinal data document detectable IgM up to 17 months after erythema migrans and 3 years after neuroborreliosis; CDC and IDSA guidance recognize antibody persistence for months to years after eradication.

Interpretation and safety of diagnostic decisions

• A positive IgM result does not establish active infection, treatment failure, or a need for treatment in isolation. Serology is not a test of cure.
• CDC advises disregarding IgM immunoblot results when symptoms have lasted >30 days. At that point, isolated IgM is more likely to represent persistent antibodies or a false-positive finding than active Lyme disease.
• Interpretation should use validated two-tier testing plus compatible manifestations, illness timing, and pretest probability. Cross-reactivity—including with relapsing fever, syphilis, rheumatoid arthritis, and Epstein–Barr virus infection—can yield false-positive Borrelia serology.
• In one referral cohort, 27.5% of patients with a positive IgM immunoblot were judged to have false-positive results, illustrating the clinical risk of treating isolated IgM as diagnostic.

Bottom line

• The claim is well supported: Borrelia-specific IgM usually arises early but can persist long after infection; particularly after 30 days of symptoms, IgM positivity alone cannot independently establish active Borrelia infection.