Ratner and his colleagues wanted to assess just how often a new bull's-eye rash is linked to a new infection or a recurrent one. To do this, they tested 22 skin or blood samples from 17 people who'd had a Lyme infection and then had a second, third or fourth episode of a new bull's-eye rash.
The researchers ran genetic tests on the samples to see if the strains of Borrelia burgdorferi were the same or different in each infection. B. burgdorferi is the bacterium transmitted by ticks to humans to cause Lyme disease.
None of the consecutive episodes of bull's-eye rashes was linked to the same strain of the bacteria.
"We found that in every single case, the subsequent infection was new," Nadelman said.
In addition, Nadelman said all of the new infections occurred during the tick-biting season -- late spring to summer -- and all of the rashes occurred at sites that were different from the initial infection. What these findings point to, he said, is a need for tick prevention.
One physician said the new findings lend more support to his current clinical practice.
"This study helps to solidify the confidence in what we're already doing," said Dr. Bruce Hirsch, an attending physician in infectious diseases at North Shore University Hospital, in Manhasset, N.Y. He said he already treats new rashes as new infections, and avoids prolonged antibiotic use in people with Lyme disease.
Hirsch added that for some people, it can take a while to get over a Lyme disease infection, even after the bacteria have been destroyed by antibiotics.
"An infection can sometimes take a toll on the body, requiring a significant recovery period, and it uses a tremendous amount of energy to get over some infections," he said.
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