The Lyme disease epidemic in the U.S. is worse—much worse—than doctors and public health officials have feared. Last year, the Centers for Disease Control & Prevention reported some 30,000 cases of Lyme disease. That number has exploded to an estimated 300,000 cases of Lyme annually, the agency reported last week. It’s not that the disease suddenly spread, but that it’s been undercounted in the past.
Scientists have long suspected that Lyme disease, the number one vector-borne illness in the U.S., is significantly underreported. “We know that routine surveillance only gives us part of the picture and that the true number of illnesses is much greater,” says Paul S. Mead, chief of epidemiology and surveillance activity for CDC’s Lyme disease program. Previous estimates of disease incidence have been based only on cases reported by doctors.
For its new estimate, CDC analyzed data from three ongoing studies. The first study involves 22 million medical insurance claims, the second relies on test results from clinical laboratories, and the third uses self-reported cases of Lyme disease from a survey of the general public.
CDC’s new estimate doesn’t surprise Lyme disease researchers. “It is generally accepted in epidemiology that only about 10% of cases are reported for almost any disease,” says Durland Fish, a professor of epidemiology at the Yale School of Public Health and an expert on tick-borne illnesses.
Still, some scientists say solid estimates on the number of Lyme disease cases can be especially difficult. Diagnostic tests have a high rate of false negatives, particularly in the early stage of infection.
Left untreated, Lyme disease can be physically debilitating and cause severe neurological problems.
The actual number of Lyme disease cases in the U.S. is likely to be even higher than 300,000 per year, says David Roth, cochairman of the Tick-Borne Disease Alliance, a nonprofit group dedicated to increased funding for research on tick-borne illnesses. “It depends on how you define the illness,” he says, adding that several tick-borne diseases similar to Lyme also go undiagnosed.
Research should focus on controlling the tick population, Fish says, because “it would not only reduce Lyme disease, but it would reduce all of the other tick-borne diseases as well.”