Can Borrelia antibodies identify an active infection?

In an older adult, a broad Borrelia antibody pattern can provide useful evidence of prior immune recognition, but it does not by itself establish that ongoing infection is responsible for current symptoms.

Serologic interpretation

• Antibodies directed at multiple distinct Borrelia antigens indicate an expanded humoral response rather than reactivity limited to one target.
• This is consistent with the characteristic expanded IgG immunoblot response in Lyme arthritis, in which patients almost uniformly show reactivity to at least 5 of 10 specified IgG bands.
• Broad reactivity is not equivalent to diagnostic confirmation on its own. Validated two-tier approaches—conventional EIA/IFA followed by immunoblot, or validated modified two-tier EIA algorithms—remain important because individual antigen responses may be nonspecific or cross-reactive.
• Relevant cross-reactive targets include OspC, BmpA, VlsE, FlaB, and p66; C6 reactivity may also cross-react with Borrelia miyamotoi. Several bands that do not meet validated criteria should not be interpreted as a positive test.

Active versus prior infection

• A positive IgM or IgG result cannot determine whether infection is currently active. Both antibody classes may remain detectable for years or decades after infection has cleared or after treatment.
• Thus, multi-antigen reactivity may reflect past, resolved, or treated infection rather than viable organisms causing present illness. Repeat serology is generally not useful for assessing cure or persistence.
• Interpretation requires a compatible clinical syndrome, examination findings, exposure history, and illness timing. Early localized disease may still be seronegative despite high overall specificity of recommended testing.

Mechanistic and practical implications

• Antibody persistence reflects durable immunologic memory, not necessarily ongoing bacterial replication.
• In selected seropositive patients with suspected Lyme arthritis, synovial-fluid or tissue PCR may be considered as an adjunct; however, persisting microbial DNA after treatment limits PCR as a stand-alone marker of active infection.

Bottom line

• Multiple Borrelia antibody specificities support broad prior immune recognition, but serology alone cannot distinguish active Lyme disease from remote or treated infection.