Oct. 5 (HealthDay News) -- Many people who believe they're suffering a relapse of Lyme disease may actually have been bitten by another tick and have a second, completely new infection, a new study suggests.

"It is striking how often re-infection appears to occur," lead author Dr. Robert B. Nadelman, professor of medicine at New York Medical College, said in a prepared statement. "Our findings support clinical evidence that a surprising number of patients experience more than one episode of Lyme disease and that recurrent infections are unrelated to the original infection."

Lyme disease, which affects about 20,000 Americans a year, is caused by Borrelia burgdorferi, a bacterium that's transmitted to humans by deer ticks. About 95 percent of patients recover completely and quickly with two to three weeks of antibiotic treatment. Left untreated, the infection usually goes away within a month. However, untreated patients can relapse and/or develop late complications that affect the joints, heart, or nervous system, according to background information in a new release about the study.

Many patients who are diagnosed and successfully treated for Lyme disease develop the infection again, likely because they live in areas where deer ticks are common, the researchers said.

They analyzed B. burgdorferi genotypes from skin biopsies of 272 people diagnosed with Lyme diseases between 1991 and 2005. The team found that some of the patients had suffered separate Lyme disease-causing tick bites.

The findings "underscore the importance of preventing exposure to ticks, by covering exposed skin, using tick repellants, and performing self-examination for ticks on a regular basis during the tick season," Nadelman said.

The findings were to be reported Thursday at the annual meeting of the Infectious Diseases Society of America, in San Diego.

SOURCE: Infectious Diseases Society of America, news release, Oct. 4, 2007