Vitality

Lyme Disease Is On The Rise In Canada, But Scientists Warn Against False-Positive Test Results

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Lyme disease is increasingly common; Canadians seeking a diagnosis from laboratories in the US should be on the lookout for possible false-positives. Joe Shlabotnik, CC by 2.0

The Canadian government reported just 128 cases of Lyme disease in 2009, yet this number quadrupled in five years, rising to 522 reported cases in 2014. With the disease becoming increasingly common north of the Lower 48, Canadians seeking a diagnosis from commercial laboratories in the United States should be on the lookout for possible false-positives. At three out of four such laboratories, one investigation found false-positive results were given to 2.5 percent to 25 percent of people without the disease.

“The serologic diagnosis of Lyme disease in Canada is best done using standard laboratory protocols as implemented by the National Microbiology Laboratory of Canada using criteria recommended by the Centers for Disease Control and Prevention (CDC),” wrote the authors of a published commentary.

However, Canada's public health care system test is also imperfect, though it is based on the most recent CDC guidelines.

Tracking Lyme Disease

Lyme disease was first reported in 1975, when a cluster of children and adults residing in the area of Lyme, Conn., began to experience uncommon arthritic symptoms. By 1977, 51 cases of “Lyme arthritis,” as doctors referred to it then, had been diagnosed. More importantly, a black-legged tick carried by deer had been identified as responsible for its transmission.

In 1982, Dr. Willy Burgdorfer, who worked at Rocky Mountain Laboratory, a National Institutes of Health (NIH) facility, discovered the bacterium responsible for the infection, Borrelia burgdorferi, named in his honor. Two years later, serology (blood) testing became available, widely so in Connecticut. Known to be imperfect at that time, this unfortunate trend has continued to this day.

One reason for some inaccuracy is that five subspecies of B. burgdorferi exist, accounting for more than 100 different strains in the U.S. and 300 worldwide. Another reason, said Dr. David Patrick, a co-author of the commentary and director of University of British Columbia’s School of Population and Public Health, has to do with the timing of the test. Speaking with The Globe and Mail, Patrick said Lyme disease tests “are insensitive in early infection (just like HIV)” because it takes time for an infected patient to produce antibodies. At later stages of the disease, though, the tests are much more accurate, “quite good” in Patrick’s words.

Tests conducted at the National Microbiology Laboratory of Canada follow the guidelines set by the CDC and so are as sensitive as tests conducted in specialty diagnostic laboratories. Though imperfect, they are the best devised to date.

“Current diagnostics are less than optimal for early disease,” wrote the authors of a 2012 report from the CDC, which reported 27,203 confirmed cases of Lyme disease and 9,104 probable cases in 2013. Meanwhile, NIH scientists continue to research new tests, new biomarkers, and the role played by immune response.

Based on all the available scientific evidence, the commentary authors recommended Canadian patients with possible Lyme disease symptoms trust the national laboratory to provide the best available information at this time. After all, one specialty laboratory in the U.S., which used in-house criteria, showed false-positive results for 57 percent of the samples taken from people without the disease.

“Mistakes in diagnosis can deprive patients of treatment specific to the true cause of their symptoms, and can result in prolonged therapy for a condition they do not have,” wrote the authors. They added that most Canadians with specialty lab results indicating Lyme disease typically have other causes for their symptoms.

Source: Gregson D, Evans G, Patrick D, Bowie W. Lyme disease: How reliable are serologic results? CMAJ. 2015.

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