About Anaphylaxis

• Triggers
• Risk factors
• Mechanisms
• Epidemiology
• Symptoms
• Diagnosis
• When to refer

Further information:

Prescribing Information

Patient Information Leaflet

Triggers

Anaphylaxis can be triggered by a wide variety of allergens, which range from very obvious to very difficult to identify. The following are some common triggers:

Foods: e.g., eggs, milk, nuts, fish, wheat, and prawns.¹,² However, any food, including fruits and vegetables, can cause anaphylaxis. Children frequently outgrow allergies to milk, soy, and eggs, but peanut, tree nut, shellfish and fish allergies tend to last a lifetime.

Food allergens account for 30% of fatal causes of anaphylaxis.³ In extreme cases, anaphylaxis can occur from kissing someone who has eaten the offending allergen, or from the food vapour in the case of cooking shellfish.

When anaphylaxis to food occurs, it does so within minutes to a few hours. Biphasic anaphylactic reactions can occur in up to 25% of fatal and near-fatal food reactions (see Mechanisms).

Medications: e.g. penicillins, cephalosporins, aspirin, NSAIDs, antimalarials, anaesthetics, sedatives, antipsychotics, antihypertensives, intravenous contrast media.⁴,⁵ Penicillin is the most common medication to cause anaphylaxis.⁶ Serious reactions to penicillin occur about twice as frequently following intramuscular or intravenous administration versus oral administration.

All doctors giving flu vaccines must have adrenaline on hand.

In contrast to food anaphylaxis, drug anaphylaxis is characterised by a high frequency of cardiovascular collapse and rapid onset (within minutes), especially in older patients.⁷

Latex: especially natural latex, commonly found in gloves, balloons, baby bath toys, belts, condoms, elastic bands, erasers, gloves, and some shoes.²,⁴ Synthetic latex appears to be less allergenic than natural latex.

Many latex examination gloves have powder inside to facilitate putting them on and taking them off. This powder absorbs latex protein so that when gloves are put on or removed, the powder and attached allergen are released into the air, thus sensitising some individuals through the respiratory or mucosal route.⁸

Repeated exposure appears to lead to a greater likelihood of sensitivity. Thus, those who have medical conditions or occupations that involve repeated, ongoing exposure to latex are at higher risk, e.g. children requiring multiple surgeries and healthcare professionals.

Some individuals with latex allergy will also have allergy to certain foods such as avocados, bananas, chestnuts, and kiwi because of cross reactivity to latex.

Insect venom: e.g. bees, hornets, wasps, and fire ants. Stings are more likely to cause anaphylaxis than bites.⁹ Anaphylaxis to insect stings has occurred in 3% of adults and 1% of children who have been stung and can be fatal even on the first reaction. Cutaneous systemic reactions are more common in children, whilst hypotensive shock is more common in adults, and respiratory complaints occur equally in all age groups.

Approximately 30% to 60% of patients with a history of anaphylaxis from an insect sting and venom-specific antibodies will experience a systemic reaction when re-stung.¹⁰

Exercise: a rare trigger, but more likely in people sensitive to certain foods (e.g. wheat, celery, and cheese) or medications if these are taken prior to exertion, even if they don’t usually produce such a reaction.⁴,¹¹Typical symptoms include extreme fatigue, warmth, flushing, pruritus, and urticaria, occasionally progressing to angio-oedema, wheezing, upper airway obstruction and collapse.

Other: less common triggers include exposure to airborne allergens (such as animal dander) and cold temperatures. Sometimes a specific cause cannot be identified and this condition is called idiopathic anaphylaxis.²,⁴

This diagnosis is pronounced after an exhaustive search for causative factors has not yielded a recognisable cause. Serum tryptase and urinary histamine levels may be useful (see diagnosis section).

There is controversy regarding the level of exposure required to trigger anaphylaxis. A highly sensitive individual may require less exposure to the offending trigger compared with a less sensitive individual.