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J Allergy Clin Immunol Pract. 2018 Nov 23. pii: S2213-2198(18)30742-6. doi: 10.1016/j.jaip.2018.11.015. [Epub ahead of print]

Emergency Management of Anaphylaxis Due to an Unknown Trigger: An 8-Year Follow-Up Study in Canada.

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McGill University, Montreal, Quebec, Canada. Electronic address:
Division of Clinical Epidemiology, McGill University Health Centre, Montreal, Quebec, Canada.
Division of Rheumatology, Department of Medicine, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
Department of Emergency Medicine, Montreal Children's Hospital, McGill University Health Center, Montreal, Quebec, Canada.
Department of Emergency Medicine, Hôpital Sacré-Coeur, Montreal, Quebec, Canada.
Department of Emergency Medicine, Hôpital Sainte-Justine, Montreal, Quebec, Canada.
Division of Allergy and Immunology, Department of Pediatrics, BC Children's Hospital, Vancouver, British Columbia, Canada.
Department of Pediatrics and Medicine, Children's Hospital at London Health Sciences Centre, London, Ontario, Canada.
Department of Pediatrics, Faculty of Medicine, Memorial University, St John's, Newfoundland, Canada.
Division of Pediatric Allergy and Clinical Immunology, Department of Pediatrics, Montreal Children's Hospital, Montreal, Quebec, Canada.



Anaphylaxis due to unknown trigger (AUT) is anaphylaxis not explained by a proved or presumptive cause or stimulus at the time of the reaction. Research describing the management and follow-up of AUT is limited.


To assess and compare the demographic and clinical characteristics and the management of adult and pediatric AUT cases across Canada.


Participants were identified between 2011 and 2018 in emergency departments at 8 centers across Canada as part of the Cross-Canada Anaphylaxis Registry. A standardized form documenting the reaction and management in children and adults was completed. Patients were contacted for follow-up to determine assessment by an allergist.


A total of 295 AUT cases (7.5%) were recruited among 3,922 cases of anaphylaxis. In the prehospital setting, children (adjusted odds ratio [aOR], 1.20; 95% CI, 1.05-1.37) and those with a known food allergy (aOR, 1.14; 95% CI, 1.02-1.28) were more likely to receive treatment with epinephrine. Children were also more likely to be assessed by an allergist after their reaction (aOR, 1.43; 95% CI, 1.13-1.81) and were more likely to have an identified trigger for their reaction (aOR, 1.35; 95% CI, 1.07-1.70). Among patients contacted for follow-up, food was identified as the cause of reaction in 11 of 76 patients. A new food allergy was diagnosed in 4 patients (2 children and 2 adults).


Our findings highlight important differences between management and follow-up of adult and pediatric AUT cases. It is crucial to follow up all cases of AUT and establish appropriate treatment and management guidelines.


Epidemiology in Canada; Idiopathic anaphylaxis; Management; Treatment


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