New Brunswick’s chief medical officer of health, Dr. Yves Léger, has delivered a new report on a cluster of almost 400 patients who had reported symptoms allegedly connected to a mystery brain disease over the past five years.

Just like a 2022 provincial government report and a scientific study published in the journal JAMA last year, the latest findings say there’s no evidence to support the existence of such a disease and that some patients have other illnesses like Alzheimer’s disease or Lewy Body Dementia.

Nearly 400 New Brunswick residents — mostly in the Acadian Peninsula and Moncton areas — have reported symptoms of what the province’s Health Department has previously called a “neurological syndrome of unknown cause.” The matter has baffled experts for years and made national and international headlines.

Below are some key dates in the development of the cluster of cases that has captured the world’s attention:

2020: Moncton neurologist Dr. Alier Marrero notices elevated levels of metals and herbicides in some patients whose ailments he is unable to diagnose. He refers the findings to the province’s chief medical officer of health, Dr. Jennifer Russell, and asks for assistance.

March 2021: Provincial health officials warn health-care workers and the public about dozens of cases of a mystery ailment impacting residents.

June 3, 2021: The province creates a committee to oversee clinical investigative work into a “neurological syndrome of unknown cause.” The heads of both provincial health authorities are named co-chairs of the team, which includes six neurologists.

Oct. 27, 2021: Public health officials rule out food and environmental exposures as potential causes of the reported brain disease. Forty-six of the 48 patients studied were referred by Marrero. The clinical review continues.

Feb. 24, 2022: The clinical review concludes there is no evidence of a cluster of patients with an unknown neurological syndrome in the province.

January 2023: Marrero raises new concerns, reports more patients with unusual symptoms, and suggests ideas about the cause. He asks provincial and federal officials investigate a link between the illness and the weed killer glyphosate.

December 2023: Dr. Yves Léger is named acting chief medical officer of health after Russell resigns.

August 2024: With patients calling for more investigations, Liberal Leader Susan Holt makes an election campaign promise to launch an “open and transparent scientific investigation” into the mystery illness if her party forms government.

Oct. 21, 2024: The Holt Liberals unseat the Progressive Conservatives and win a majority government.

March 6, 2025: Léger becomes the permanent chief medical officer of health.

March 27, 2025: Léger announces the government’s new investigation, saying there’s enough verified patient information to work with the Public Health Agency of Canada to analyze the data from 222 patients.

May 27, 2025: Léger says the initial analysis is complete and has been submitted to the federal public health agency for scientific review.

Sept. 5, 2025: The provincial government begins finalizing its report and asks Ottawa’s health agency for more support, including a review of all data collected, following a request from patient representatives.

Jan. 23, 2026: Léger releases the final report, finding no evidence of the existence of a mystery illness. He makes several recommendations, including that patients receive more followup testing. The Public Health Agency of Canada will conduct a separate review of all the data collected as part of Léger’s investigation. Patient advocates renew calls for a new review — excluding New Brunswick officials — with a team of neurologists.

This report by The Canadian Press was first published Jan. 23, 2026.

Devin Stevens, The Canadian Press