Final answer:
Serologic assays for Lyme disease are insensitive during the first several weeks of infection, requiring a two-step testing process including EIA and Western blot tests for accurate diagnosis.
Step-by-step explanation:
Serologic assays for Lyme disease are insensitive during the first several weeks of infection. During this early stage, the body has not yet produced enough antibodies against the Borrelia burgdorferi bacteria to be detected by enzyme immunoassay (EIA), which is the first blood test usually administered. A subsequent blood test, often an immunoblot or Western blot test, may be needed for confirmation, particularly if early test results are indeterminate or if there's a high clinical suspicion based on symptoms and history of tick exposure.
The Western blot is more specific but can still yield false positives, which is why results should be interpreted carefully. In the case of Ximena, mentioned earlier, although her initial EIA test results were indeterminate likely due to a recent infection, the CDC recommends two-step testing, which for her confirmed the Lyme disease diagnosis.