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.