Background: Cleaning Solution Mistakenly Served at McDonald’s Drive-Thru
In a recent decision from the Ontario Superior Court of Justice, the court reaffirmed the importance of proving causation in personal injury claims—even in cases where liability is admitted. The case, MacNeill v. McDonald’s Restaurants of Canada Limited, 2025 ONSC 3780, involved a woman who was mistakenly served a cleaning solution in a coffee cup at a McDonald’s drive-thru in Orillia, Ontario.
The incident occurred on October 1, 2015, when the plaintiff received a paper cup containing a diluted delimer solution, a chemical used to clean coffee machines. McDonald’s acknowledged the error and accepted liability for the mix-up. However, the dispute centered on the extent of the plaintiff’s injuries and whether they were caused by the ingestion of the cleaning fluid.
The Plaintiff’s Claims: Physical and Psychological Harm
The plaintiff alleged that the incident caused a range of serious injuries, including chemical burns to her throat, muscle tension dysphonia (MTD), chronic pain, and a persistent raspy voice. She also claimed that the ingestion exacerbated pre-existing injuries from a 2009 motor vehicle accident, ultimately rendering her unable to continue working in her customer service role.
Her damages claim was substantial:
- General damages of up to $125,000
- Past income loss exceeding $340,000
- Future income loss of over $1 million
- Additional claims for loss of competitive advantage and future care costs
The Defence: No Causal Link Between Incident and Alleged Injuries
While McDonald’s accepted responsibility for the initial error, it disputed the severity and cause of the injuries. The defence emphasized that the delimer solution was food-safe, with a pH level similar to lemon juice, and argued that it could not have caused the chemical burns or long-term voice issues alleged by the plaintiff.
The court was tasked with determining whether the ingestion of the cleaning solution was the “but for” cause of the plaintiff’s injuries. The “but for” test is routed in legal principles from Athey v Leonati, 1996 CanLII 183 (SCC), which has become a fundamental test in tort law. The plaintiff bore the burden of proving, on a balance of probabilities, that the incident caused the harm she described.
The Court’s Findings: Temporary Discomfort, Not Lasting Injury
Justice D.L. Corbett undertook a detailed review of the evidence, focusing on whether the ingestion of the cleaning solution caused the serious and lasting injuries alleged by the plaintiff. While the court accepted that the plaintiff did consume a small amount of the delimer solution and experienced immediate symptoms—such as nausea, a burning sensation, and gastrointestinal upset—it found that these effects were short-lived and did not result in any permanent harm.
The plaintiff’s claim of chemical burns was not supported by contemporaneous medical records. Emergency department notes from the day of the incident indicated no visible signs of burns or acute injury to the throat or mouth. Moreover, follow-up medical assessments did not reveal any objective evidence of tissue damage consistent with chemical exposure.
The court also scrutinized the plaintiff’s diagnosis of MTD, a voice disorder she attributed to the ingestion. Expert testimony revealed that MTD is typically associated with psychological stress and vocal strain, rather than chemical injury. Given the plaintiff’s history of anxiety and prior trauma from a motor vehicle accident, the court found it more likely that her voice issues stemmed from pre-existing conditions rather than the McDonald’s incident.
Justice Corbett noted inconsistencies in the plaintiff’s testimony and highlighted the absence of a clear, continuous medical narrative linking the ingestion to the long-term symptoms. The court emphasized that the burden of proof lies with the plaintiff to establish causation on a balance of probabilities. In this case, that burden was not met.
Damages Awarded: A Fraction of the Claim
In the end, the court awarded the plaintiff $5,000 in general damages, recognizing the distress and discomfort caused by the ingestion but rejecting the broader claims for long-term harm and financial loss.
Key Takeaway: Causation Remains Central in Personal Injury Law
This case serves as a clear reminder that even when liability is admitted, plaintiffs must still establish a causal link between the defendant’s conduct and the alleged harm. Courts will closely scrutinize medical evidence and expert testimony, particularly when pre-existing conditions are involved.
For personal injury practitioners, MacNeill reinforces the importance of preparing robust, causation-focused evidence, especially in cases involving unusual or low-impact incidents.
At Flaherty McCarthy, we are deeply committed to upholding the principles of fairness, diligence, and client-focused advocacy in personal injury law. We understand that every case is unique, and we approach each matter with the care and precision it deserves, whether navigating complex causation issues or advocating for meaningful compensation. Our team remains dedicated to helping clients understand their rights, build strong evidence-based claims, and achieve outcomes that reflect both the law and their lived experiences.
