Patients suffering from persistent symptoms they believe to be caused by a past episode of Lyme disease aren’t helped by long courses of antibiotics, according to a new study.

Why it matters:

Of the tens of thousands of Lyme infections worldwide every year, some 4 to 20 percent of people continue to suffer symptoms they attribute to the disease — such as arthritis, neuropsychological disorders, or fatigue — for years. But it’s an unsettled question whether these patients’ symptoms are connected to Lyme disease and what to do about them.

Doctors sometimes prescribe long courses of antibiotics, but the research on the effectiveness of this practice is patchy. According to the Centers for Disease Control and Prevention, studies have not shown antibiotics to be effective in treating these long-term symptoms.

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The nitty gritty:

Researchers studied over 200 individuals in the Netherlands who had been suffering from symptoms they attributed to Lyme disease for an average of two years. Everyone was given a strong antibiotic for two weeks, and then they were split into groups given either no drugs or given different antibiotics for a subsequent three months. Everyone reported a quality-of-life improvement from the beginning of the trial, but the drugs given after the preliminary antibiotic did not have an additional effect.

“It’s been unknown whether the prolonged treatment with antibiotics would have any benefit over a standard course of antibiotics,” said Dr. Bart Jan Kullberg, the study’s primary investigator and a professor at Radboud University Medical Center in the Netherlands. “And basically what we’ve shown in this trial is that it didn’t.” The study was published in the New England Journal of Medicine.

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But keep in mind:

Outside researchers cautioned that the results from this study might not be generalizable because of how varied the participants were.

“They mixed apples and oranges and bananas together in this study,” said Dr. John Aucott, director of the Lyme Disease Research Center at Johns Hopkins University School of Medicine. For instance, 10 percent of the people in the study had never been treated for Lyme disease, while others had been suffering symptoms for years. Those two groups might respond differently to antibiotics, but the results were all grouped together in the paper.

What’s next?

Kullberg said it’s still an open question why some patients are cured of Lyme disease and others experience symptoms for years. He is working on prospective studies of patients suffering from Lyme disease to try to answer this question.

The bottom line:

Scientists still don’t know why some people who contract Lyme disease continue to suffer symptoms they think are related to the Lyme disease years after being treated for the original disease. But taking antibiotics for an extended period of time — after taking strong antibiotics for two weeks — doesn’t seem to help those symptoms.

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Correction: This story originally misstated the name of the journal in which the study was published. It has been updated.