Incidence of anaphylaxis in hospitalized patients.

Background: Only two studies have analyzed the incidence of anaphylaxis during admission to hospital. We have analyzed the incidence of anaphylaxis among hospitalized patients and determined the timing of and risk factors for episodes of anaphylaxis.

Methods: Our study was performed between 1999 and 2005. We used the definition of anaphylaxis of the NIAID-FAAN symposium. Cases of anaphylaxis were extracted from an official database of discharge diagnoses coded according to the International Classification of Diseases, Clinical Modification, Ninth Revision (ICD-9-CM), Sixth Edition. Specific and generic codes related to anaphylaxis were chosen. This strategy revealed 83.3% (95% confidence interval, CI, 47-99%) of all episodes of anaphylaxis in a pilot study. The incidence of episodes of anaphylaxis and the hazard ratios were calculated for the different variables.

Results: We observed a crude cumulative incidence of 1.5 episodes of anaphylaxis (95% CI, 0.9-1.9) in 5,000 admissions. The cumulative incidence according to the Standardized European Population was 1.6 cases in 5,000 admissions (95% CI, 0.8-2.3). Cox regression analysis showed that anaphylaxis occurs mainly in young people (0.97; 95% CI, 0.95-0.99) and its incidence differs according to the clinical unit. The Vascular Surgery Unit had the highest incidence rate (hazard ratio 7.7; 95% CI, 2.1-28.6). Males had a lower risk of suffering from anaphylaxis than females (0.5; 95% CI, 0.2-0.9).

Conclusions: Anaphylaxis is a very rare event among hospitalized patients. Female gender, young age and admission to the Vascular Surgery Unit favored the occurrence of episodes of anaphylaxis among hospitalized patients.