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A population-based study of the incidence, cause, and severity of anaphylaxis in the United Kingdom.

BACKGROUND
Anaphylaxis is an acute and potentially fatal systemic reaction usually caused by mast cell-mediated release of histamine. Symptoms can vary in onset, appearance, and severity. Some common symptoms include weakness, dizziness, flushing, angioedema, urticaria, nasal congestion, and sneezing. Severe symptoms include upper respiratory tract obstruction, hypotension, vascular collapse associated with angioedema and urticaria, gastrointestinal distress, cardiovascular arrhythmias, and/or arrest.


METHODS
We conducted an observational follow-up study encompassing approximately 8 million person-years based on the UK General Practice Research Database for the period January 1, 1994, to December 31, 1999, which quantified the frequency, type, and severity of a clinical diagnosis of anaphylaxis.


RESULTS
Based on 675 cases of anaphylaxis, we estimate the incidence to be 8.4 per 100 000 person-years. Approximately 10% of cases had hypotension and shock that required urgent treatment. The most common causes were insect stings and oral medicines.


CONCLUSION
Anaphylaxis is an uncommon illness that has multiple causes and can be life-threatening.