The study, published in the New England Journal of Medicine, is more evidence that proper antibiotic treatment is effective and that bacteria do not hide in the body for years, waiting to make a subsequent appearance.

But the findings also reveal that people who are outdoors in areas where Lyme disease is common must be careful to avoid tick bites even if they've had the disease before. One infection does not confer immunity against another.

"It provides compelling evidence that these are reinfections, not relapses," lead researcher Dr. Robert Nadelman of New York Medical College in Valhalla told Reuters Health.

Not only did genetic testing of the bacteria behind each infection show subsequent Lyme rashes came from different strains, "all the infections pretty much occurred in the summer months when the ticks are active, they were a year or more apart and the rash was at a different site than the original," he said.

In some cases, the central spot of the rash showed direct evidence of a new tick bite.

In addition to the bulls-eye rash, Lyme disease can initially cause fever, headache and fatigue. In some instances it can lead to serious heart and nerve problems and arthritis.

Ticks that transmit the bacteria behind Lyme disease are found in Europe, Asia and North America. In the U.S., the disease is concentrated in northeastern states, with tens of thousands of cases reported annually.

Antibiotics usually cure it quickly, but some patients report Lyme disease symptoms well after treatment.

Studies have shown that in those people, additional antibiotic treatment is of little use. There's also no evidence in favor of long-term courses of antibiotics for treating Lyme disease and preventing recurrences.

RELAPSES UNUSUAL

In the unusual instance where there is a Lyme disease relapse, it typically happens within a few weeks, Nadelman said. One U.S. study showed 15 percent of people who develop the infection once risk getting it again within five years.

In their study, Nadelman and his colleagues found that a person's second episode of Lyme disease typically occurred about four years after the first, although the range was one to 15 years.

Some of the nine men and eight women they studied had more than two infections, so there were 22 paired consecutive episodes in all.

In each case, none of the infections involved the same strain of bacteria that had caused the previous rash.

The findings provide more evidence that antibiotics are successful at clearing the bacteria responsible, the researchers said.

"One course of antibiotics should be enough," said Nadelman.

There are some people who claim to be suffering from chronic Lyme disease because they have unexplained pain, fatigue or nerve problems. In some of those cases, there's no evidence they were actually infected, Dr. Allen Steere of Massachusetts General Hospital in Boston wrote in an editorial published with the study.

Steere is the researcher who first identified Lyme disease.

"Although… infection may persist for years in untreated patients, the weight of evidence is strongly against persistent infection as the explanation for persistent symptoms in antibiotic-treated patients with Lyme disease," Steere wrote.

Steven Norris from the University of Texas Health Science Center at Houston, who was not involved in the research, told Reuters Health the new study doesn't address symptoms beyond the bulls-eye rash.

"There are two philosophies," he said. "There is the philosophy that once the patient has been treated for three to six weeks, it's rare that the disease will reoccur. There's another group that thinks it's quite common, and therefore long-term therapy is required," Norris added - even if the data don't prove it's effective.

SOURCE: bit.ly/T3qePN New England Journal of Medicine, online November 14, 2012.

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