This study found that the rate of hospitalizations for anaphylaxis increased almost two-fold from 1991 to 1995. Reasons for the increase are not completely understood, although a number of factors associated with the "Western lifestyle" have been implicated, such as changes in diet and the increasing use of therapeutic drugs.

Anaphylaxis is an allergic reaction in which large quantities of histamine are released by the body, causing either local or widespread symptoms. A more severe form is anaphylactic shock, which can result in swelling (edema), heart failure, and sometimes death.

Compiling the records of 32.4 million hospital discharge records, researchers found an increase from 5.6 instances of anaphylaxis per 100,000 discharges in 1991-2 to 10.2 in 1994-5. The increase was seen across all age groups, in both sexes, and within all four regions of England.

The most common cause of anaphylaxis was therapeutic drugs (62%), followed by food (15%) and insect venom (11%). Although these percentages remained fairly constant throughout the four years, for some subcategories increases were noted above the overall increase in anaphylaxis. One of these increasingly noted causes of anaphylaxis is designated in the records as "bacterial, biological, and other vaccines."

The authors also noted that this rate of hospital admissions for anaphylaxis is likely to be a substantial underestimate, since many cases are treated in emergency settings and do not result in hospital admission.

British Medical Journal 2000; 320: 1441