Does broad Borrelia IgG reactivity indicate prior exposure rather than active infection?

Broad Borrelia IgG reactivity is most reliably interpreted as evidence of prior immune recognition, not as a stand-alone marker of current infection. This distinction is particularly important when testing is obtained outside a clinically compatible, exposure-plausible syndrome.

Serologic interpretation

• Multi-antigen IgG reactivity is consistent with prior Borrelia antigen exposure and durable humoral memory. In standard two-tier testing, an IgG immunoblot requires reactivity to at least five specified antigens.
• Persistence is common long after illness resolution: 10–20 years after treated Lyme disease, IgG remained positive in 25% of people with prior early Lyme disease and 62% with prior Lyme arthritis. Persistent responses included DbpA, BmpA, FlaB, p58, and p93.
• C6/VlsE-directed IgG may decline after treatment but can remain positive, so neither broad IgG reactivity nor a residual C6 result can date infection, demonstrate treatment failure, or function as a test of cure.

Active-infection assessment

• A single positive antibody result—including broad IgG reactivity—does not demonstrate viable organisms or active B. burgdorferi infection. Serology measures host response, and both IgG and sometimes IgM may persist for years or decades after eradication or successful therapy.
• Interpretation requires compatible manifestations, symptom timing, and epidemiologic exposure likelihood. In a low-incidence cohort without endemic travel, serology’s positive predictive value was only 10%.
• Serial evidence can add context: a broad, evolving IgG response with rising titers during a compatible illness supports active infection, but is not established by one sample. Isolated IgM after >30 days of symptoms is particularly unreliable.

Bottom line

• Broad Borrelia IgG strongly supports previous antigen exposure and durable immune memory, but alone cannot establish active infection or persistent bacteria; clinical syndrome and exposure context determine its practical meaning.