When the Centers for Disease Control and Prevention (CDC) estimated last summer that the number of people diagnosed with Lyme disease each year was 300,000 — 10 times as high as the official counts — the agency must have expected headlines, and it got them. The alarmingly high figure justified assertions by patient advocacy groups that the 30,000 cases reported annually were just the tip of the iceberg.
Lyme disease is caused by a bacterium, Borrelia burgdorferi, which is transmitted by black-legged ticks. Infection results in fever, headache, fatigue and, in many cases, a distinctive oval rash called an erythema migrans. Untreated, Lyme may advance to painful complications of the joints and nervous system. The disease is concentrated in the Northeast and upper Midwest, and in parts of the Pacific Northwest. The CDC is notified of cases by doctors, laboratories and local health departments.
