The Public Health Agency of Canada (PHAC) says it has found no evidence of a mystery brain disease that was allegedly affecting hundreds of New Brunswick residents.
A similar report from the province released in January, as well as a study published in 2025 in the journal JAMA Neurology, also concluded there was no such evidence.
Patients have told Global News they have been dealing with frequent seizures, confusion, spasms and tremors.
Dr. Alier Marrero, the physician who first brought forward the concerns about a cluster of cases in 2020, has theorized herbicides and metals in patients may be involved.
He told Global News last year he had evaluated hundreds of patients — estimated to be around 400 — and found a “significant amount of unequivocal, sometimes critical environmental exposure evidence, as well as rare autoimmune markers in many of them.”
Global News reached out to Marrero for comment on this latest report but has not received a response.
The PHAC report, which was released last month, said the agency “did not find evidence of an unusual pattern of neurological disease” after meeting with the reporting neurologist, consulting with patients and family members, examining population health trends and analyzing patient data.
PHAC reviewed and assessed data for 210 of the patients who were believed to be part of the cluster.
“While considerable information was available for these patients, including extensive medical testing, the data did not include the clinical neurology interpretation needed to define a common health event, such as a diagnosis or well defined syndrome, for most patients,” the report noted.
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Of the small subset of patients who died, the report said diagnostic information from death certificates identified “a range of known neurological and non-neurological diagnoses” rather than a “common health event.”
Sarah Nesbitt of Canaan Station, N.B. says she became very ill in the summer of 2020 and was referred to Marrero in 2021. She’s long fought for these investigations, alongside other patients and family members, and says many of them found this report to be “limited and frustrating.”
“I hope patients get actual help. Diagnosed and a treatment that helps. So many have gone so long without any of this,” she told Global News.
“The suffering is beyond comprehension. No human should be left to suffer for so long.”
In a summary of its report, PHAC said its finding “does not mean that patients’ symptoms or experiences are not real.”
“Many individuals continue to face significant health challenges, and some are still seeking answers about their condition,” it read.
The agency recommended that health officials continue to communicate with patients and conduct medical follow-ups for those who haven’t received a diagnosis.
“While there is no basis for a new investigation, public health could reduce uncertainties by reviewing new medical diagnoses,” the agency added.
It said officials should keep collecting information in the event that new evidence comes to light suggesting a common cause in a subgroup of patients.
Nesbitt says she’s encouraged by the fact the agency is urging the province to improve the care these patients are receiving, and to be more diligent in collecting data.
“The main difference from the previous reports issued by (the provincial government) is that at least they are not pretending that they have final answers. They basically say that they don’t have enough information to draw any firm conclusions,” she said.
Stacey Quigley Cormier, who became an advocate after her stepdaughter became ill, told Global News she hopes the province brings in a comprehensive reassessment process.
“Patients need an opportunity for their full medical histories, symptoms, clinical findings, and potential contributing factors to be carefully considered,” she said in an email.
Chief Medical Officer of Health responds
New Brunswick began investigating what were then 48 patients with neurological symptoms in 2021 under the previous Progressive Conservative government.
But the Blaine Higgs government said in 2022 that it found no evidence of a common illness and ended the investigation.
The current Liberal government promised during its 2024 election campaign it would reopen the investigation. New Brunswick’s chief medical officer of health, Dr. Yves Léger, announced in March 2025 that his office would take on reviewing 222 files, along with PHAC.
Léger’s report, which was released in January of this year, said there was no evidence of a mystery brain disease.
It said despite “many significant limitations” in terms of data and testing results, the team was able to conclude that the “investigation does not find evidence of a widespread issue among this patient group.”
In a statement on Friday, Léger thanked the PHAC for its work on the file.
“Our primary concern has been, and remains, the well-being of the affected patients. We will continue to work closely with the regional health authorities to ensure patients have access to the care and support they need,” he wrote.
“We have accepted PHAC’s recommendations, and our focus remains on supporting appropriate patient care and ensuring the needs of those affected remain at the forefront of our response.”
— with a file from Heidi Petracek
© 2026 Global News, a division of Corus Entertainment Inc.
