Published: November 14, 2012

When people who have been treated for Lyme disease  recover but later come down with its symptoms again, is the illness a relapse or a new infection?

The question has lingered for years. Now, a new study finds that repeat symptoms are from new infections, not from relapses.

The results challenge the notion, strongly held by some patients and advocacy groups, that Lyme disease, a bacterial infection, has a tendency to resist the usual antibiotic  treatment and turn into a chronic illness that requires months or even years of antibiotic therapy.

The conclusion that new symptoms come from new infections is based on genetically fingerprinting the Lyme bacteria in people who have had the illness more than once, and finding that the fingerprints do not match. The result means that different episodes of Lyme in each patient were caused by different strains of the bacteria, and could not have been relapses.

The study, by researchers at the University of Pennsylvania and New York Medical College, in Valhalla, was published online on Wednesday in The New England Journal of Medicine.

An estimated 20,000 to 30,000 cases of Lyme disease occur each year in the United States. The disease is caused by a bacterium, Borrelia burgdorferi, that is carried by deer ticks. It often begins with an expanding zone of red skin — a symptom called erythema migrans — around the tick bite, but sometimes in other areas too. Fever, headaches, fatigue and aches and pains often follow.

Untreated, the disease can cause heart and neurological problems and arthritis, with symptoms that can come and go for years. Advanced cases that have gone months or years before being treated are most likely to result in persistent arthritis.

But when the disease is detected earlier, treatment with an antibiotic, usually two to four weeks of doxycycline, can get rid of the bacteria, according to infectious disease experts. Even advanced cases can be cleared by the drugs, doctors say, though an extra month or so of treatment may be needed. Symptoms like pain and fatigue can linger even after the bacteria are gone, possibly because the infection caused abnormalities in the immune system.

However, some doctors, patients and advocacy groups think that the bacteria themselves can somehow hang on despite treatment, even in cases caught early, and cause a chronic infection that requires long-term treatment with antibiotics. In some cases, people with unexplained pain, fatigue and cognitive problems have been told they had chronic Lyme disease even though blood tests found no evidence of the infection.

Several controlled studies have found that long-term antibiotics did not help people who had already been treated for Lyme disease but had such lingering problems.

Despite the data, the belief has hung on that Lyme disease bacteria can cause a chronic infection even after treatment.

The researchers who conducted the new study wanted to test that idea by finding out whether people who had repeated bouts of the disease were actually having relapses. They identified 17 patients who had erythema migrans — the rash — more than once between 1991 and 2011. Most had it twice, at least a year apart, but a few patients had it three times and one had four cases. Many had other symptoms as well, and more than half had signs of widespread systemic infection. All were treated, and recovered fully.

Lyme bacteria were grown from skin or blood samples taken from the patients when they had the rash, and the researchers analyzed a bacterial gene that varies from one strain to another. For each patient, they compared the genes from different cases of the rash. The genotypes did not match, which the researchers said proved that each rash represented a new infection, not a relapse.

In an editorial accompanying the article, Dr. Allen C. Steere, a Harvard professor who was the first to identify Lyme disease, said the new study supported previous research suggesting that new infections, not relapses, were the cause of new symptoms in people who had taken antibiotics to treat earlier cases of the disease.

Dr. Steere acknowledged that symptoms, sometimes disabling ones, do linger for months after treatment in as many as 10 percent of patients. Doctors do not know why. But, Dr. Steere said, “antibiotics are not the answer.”

New York Times