Characteristics of study sample.

* Lyme disease sample includes only those persons with a test order and antibiotic treatment within 30 days of the test order, a diagnosis and antibiotic treatment within 30 days of the diagnosis, or a diagnosis, test order and antibiotic treatment within 30 days. The Lyme disease sample includes only those with 18 consecutive months of enrollment, including a 6-month “clean period” of enrollment prior to Lyme disease episode in which they were neither diagnosed with nor tested for Lyme disease.† Lyme disease and control samples are restricted to persons under 65 years of age, with commercial health insurance plans.‡ Controls were matched to Lyme disease cases on age, sex, region, payer and enrollment year. Control group includes only those with 12 consecutive months of enrollment in a commercial health insurance plan. Control group was restricted to persons with outpatient costs greater than $0.Characteristics of study sample.