Can persistent Borrelia IgG distinguish active from resolved Lyme infection?

Borrelia serology is best interpreted as evidence of immune exposure, not a direct measure of viable organisms or treatment response. This distinction is particularly important when evaluating possible recurrent or persistent symptoms after prior Lyme disease.

Serologic interpretation

• Borrelia burgdorferi–specific IgG can persist for years to decades after eradicated infection. In long-term follow-up 10–20 years after treated Lyme disease, two-tier IgG remained positive in 62% of people with prior Lyme arthritis and 25% with prior early Lyme disease.
• Consequently, persistent IgG cannot distinguish active infection from resolved infection or serve as a test of cure. A positive two-tier result may support prior exposure in the appropriate epidemiologic and clinical setting, but does not independently establish current disease or treatment failure.

Bloodstream-infection testing

• Negative IgM and negative blood PCR provide limited, timing-dependent evidence against current bloodstream infection, rather than definitive exclusion.
• IgM generally develops about 1–2 weeks after infection. Its absence is more informative in established, untreated early illness than during the first days of symptoms; early antibiotics can also attenuate or prevent seroconversion.
• Blood PCR directly tests for circulating Borrelia DNA, but sensitivity in early disease is only approximately 33.8–62% (often cited around 30–50%). Thus, a negative result only modestly reduces the likelihood of spirochetemia.

Mechanistic context

• Spirochetemia is typically transient and low-level. Organism DNA may therefore be absent or below assay detection in a blood sample despite acute infection, explaining why blood PCR has limited sensitivity while a positive result is generally specific.

Bottom line

• Persistent IgG strongly supports prior immune exposure but cannot identify active infection. Negative IgM and blood PCR do not support ongoing bloodstream infection, yet neither rules it out—especially very early after symptom onset or after antibiotics.