Canada's National Microbiology in Winnipeg made the mistakes in tests starting about six months ago, the Canadian Broadcasting Corp. reported Friday.
"There are 24 individuals who we reported out falsely, [giving] negative test results," said Dr. Frank Plummer, scientific director of the National Microbiology Laboratory. "They should have been reported as positive."
Without antibiotic treatment, Lyme disease can cause fatigue, chills, fever, headache, muscle and joint pain and memory or neurologic problems that can linger for months or years.
Of those misdiagnosed, 16 people sought treatment despite the negative test result, two never fell sick enough to seek treatment and one is going to get treatment, officials said.
The people are residents of Manitoba, Quebec and Nova Scotia, the Public Health Agency of Canada said, and provincial health officials are working to inform those affected through their family doctors.
The mistakes occurred as the lab evaluated a new test kit that uses an automated reader, Plummer said.