Manitoba Lyme cases far higher than official count, study finds
Lyme is widely recognized as an underreported illness. A 2015 American study shows cases in the U.S. were likely 10 times higher than reported. The researchers wanted to see whether a similar gap exists in Manitoba.
The true number of Lyme disease cases in Manitoba is likely at least five-and-a-half times higher than the official figure, according to a new study.
A team of eight researchers led by Winnipeg public health physician Richard Rusk estimated there was an average of 165 cases a year of Lyme disease in the province between 2009 to 2018. That compares to just 30 cases a year reported by Manitoba Health’s surveillance system.
“Further research would be beneficial to explore the level of underreporting in other provinces to enhance our understanding of the true burden of this infection across Canada,” the paper says.
Citation
Rusk R, Gasmi S, Bourgeois A-C, Whitlock M, Detillieux GR, Stimpert K, Buckeridge D, Koffi JK. 2025 Jan 6. Perspective: Incidence of Clinician-Diagnosed Lyme Disease in Manitoba, Canada 2009–2018. Vector-Borne and Zoonotic Diseases. doi:https://doi.org/10.1089/vbz.2024.0088.
Since 2009, doctors and laboratories across Canada have had to report confirmed and probable cases of Lyme disease to their regional health departments. Manitoba Health combines that data with reports on tick populations to estimate the number of Lyme disease cases.
The official figures show that during the 10-year study period, Lyme disease cases jumped from 0.40 per 100,000 population to 3.97 per 100,000 population – a ninefold increase. But Lyme is widely recognized as an underreported illness. For example, a 2015 American study shows cases in the U.S. were likely 10 times higher than reported. The authors wanted to see whether a similar gap exists in Manitoba.
In a first for a Canadian study, they attempted to find a more accurate figure by combing through data generated during the routine administration of health care programs. The Manitoba Centre for Health Policy database records information for virtually all contacts with the provincial health care system, including physicians, hospitals and pharmaceutical prescriptions.
To find potential cases, the authors searched for physician diagnostic codes that might indicate a case of Lyme disease. Over the 10-year study period, they found 3,317 unique potential cases of the illness. Next, the researchers looked for antibiotic prescriptions among those cases. They removed any patient who was not prescribed at least seven days’ worth of antibiotics within 30 days of the onset of symptoms – the standard treatment for Lyme. That resulted in 1,658 total cases of Lyme disease over 10 years – an average of 165 a year.
The study shows that more than two-thirds of the Lyme cases occurred between May and July, the peak activity period for the nymph stage of the blacklegged tick in the province. It also found that childhood infections were most common between ages 5 and 9 years. For men, infections reached their peak from ages 65 to 84 and for women, the peak age range was 50 to 74.
CanLyme President Janet Sperling says it’s likely that the study still underestimates the actual number of cases of Lyme disease. “There is no effort to consider underreporting of true cases of Lyme by those people who decided not to seek medical care or who went to the US or another country,” she points out. “These people just magically disappear from the discussion. The entire paper only considers numbers in databases.”