New Lyme disease assay may simplify laboratory testing. (Simple, Rapid, Easily Automated).

NEW YORK -- New enzyme-linked immunosorbent assays that detect a protein on the surface of the Borrelia burgdorferi spirochete may significantly curtail the need for confirmatory Western blotting in the serologic diagnosis of Lyme disease, Dr. Barbara Johnson said at an international conference on tick-borne diseases sponsored by Imedex.

Current recommendations for Lyme disease diagnosis call for two-tiered testing, starting with enzyme-linked immunosorbent assays (ELISA), when circumstances are clinically suggestive. (See box.) If results are indeterminate, a Western blot should be done, according to clinical guidelines published by the American College of Physicians (Ann. Intern. Med. 127[12]:1106-08, 1997).

Two-tiered serology has high diagnostic specificity and high sensitivity in later stages of disease but "leaves quite a bit to be desired for early disease," said Dr. Johnson of the Centers for Disease Control and Prevention. The sensitivity in acute disease is only about 30%.

The new tests detect IgG antibodies to the C6 peptide component of the variable surface antigen of B. burgdorferi. Unlike the two-tiered approach, which cannot distinguish between active and past infections, the new tests are sensitive only to IgG antibodies generated during active infection, according to the National Institute of Allergy and Infectious Diseases, which provided funding for the test's development.

In a study evaluating the diagnostic performance of this assay, 210 serum samples were collected from patients with clinically diagnosed Lyme disease in various stages. The sensitivities for acute, convalescent, and late-phase specimens were 74%, 85%-90%, and 100%, respectively (J. Chin. Microbiol. 37[12]:3990-96, 1999).

The study also tested 176 serum samples from patients in a nonendemic area who were hospitalized for conditions including spirochetal infections or autoimmune or neurologic diseases; overall specificity was 99%.