OTTAWA — The Public Health Agency of Canada says a review of its Lyme disease testing methods has turned up 24 patients in five provinces who received false-negative test results.

The testing was done at the agency's National Microbiology Laboratory in Winnipeg. The review, a quality control analysis, looked at more than 1,500 samples tested for Lyme disease and discovered the 24 incorrect test results last month.

In a statement Friday, PHAC said doctors for the 24 patients have been notified.

Lyme disease is caused by a bacterium spread through the bite of certain types of ticks. The infection, which causes such symptoms as fever, headache, fatigue and often a bull's-eye-like skin rash at the bite site, can usually be treated successfully with antibiotics.

Left untreated, the infection can spread to joints, the heart and the nervous system.

Patient blood samples are normally sent to provincial or territorial labs for testing, and those labs will often send any positive test results to the Winnipeg lab for confirmation.

The agency said it's continuing to work with the five affected provinces to ensure that doctors and their patients are notified of the revised test results so that patients can get appropriate treatment, if any is required.

The cause of the false-negative test results is being investigated.