Dr. Andy

Reflections on medicine and biology among other things

Wednesday, November 02, 2005

Fatal reactions to food

Fatal and near-fatal reactions in food allergic patients are the one thing that really makes allergists nervous. Having food allergy, or being the parent of a food allergic child is a bit like being an anesthesiologist or airplane pilot: 99% calm punctuated by 1% sheer terror. Asthma, in contrast, is much more up and down, with less explosive onset of symptoms.

A new study from England looks at the number and characterisitics of severe reactions to food in pediatric allergic patients. The authors used database searches and letters to pediatricians to try and find every case resulting in admission to the hospital. Any such search is likely to miss some cases, although one would expect they would be the less severe ones.

They divided reactions into fatal, near fatal, severe, and non-severe. The definition of fatal is obvious. Near fatal reactions were those requiring intubation, which is a pretty high standard. Severe reactions met one of the following criteria:
1. Cardiorespiratory arrest (patient stopped breathing, heart stopped beating or both)
2. Need for inotropic support (special meds had to be given to keep blood pressure up or heart beating effectively)
3. Fluid bolus of 20mg/kg or more (usually a sign of hypotension aka low blood pressure)
4. More than one dose of epinephrine
5. More than one treatment with bronchodilator (usually albuterol or salbumatol as they call it in the UK. This indicates ongoing wheezing).
Non-severe reactions were ones that didn't meet the severe criteria.

These criteria are okay, but the definition of "severe" is quite broad. I'd argue that cardiorespiratory arrest is "near fatal" because without intervention they would likely have died. On the other hand getting 2 doses of epinephrine or 2 albuterol treatments is not that remarkable. Many patients with asthma seen in the emergency department get a standard regimen of 3 albuterol treatments and are then discharged home. I suspect some kids who would meet their standards for severe reactions were not admitted.

Using their criteria they identified 3 fatal, 6 near-fatal, 58 severe and 171 non-severe reactions. Their data covers aobut 13 million kids (<16) over 3 years for 50 million kid-years. So death from food allergy was about a 1 in 1.7 million event. Obviously, the risk is much higher among kids with known food allergy.

Although peanut causes the most consternation among parents and allergists, only 1/3 fatal reactions was to peanut, the other two being milk. In the 9 combined fatal and near-fatal cases 3 were due to milk, only one clearly to peanuts although another was to walnuts and 2 were likely peanut (one kid with known peanut allergy ate a chocolate bar with nuts and another kid wiht no history of allergies ate at a Chinese restaurant). Unfortunately they didn't follow up on the kids without a clear cause to see what testing showed (i.e. if the kid who reacted at a Chinese restaraunt was peanut allergic on testing in follow up that would be the presumed trigger).

Their data contrast a bit with a famous series from the US where peanut and tree nuts were responsible for 10/13 reactions. In the US series, delay to giving epinephrine seemed to be an important risk factor for fatal reactions (vs. near-fatal) whereas in the present study it didn't seem to matter. Only 1/3 fatal reactions got epinephrine at home, one died en route to the hospital and never got it and one got it only on arrival to the hospital after arresting in the hospital. Likewise, only 2 of the 6 near fatal reactions had epi at home and those didn't have it with them when they had their reaction. To an allergist who diligently prescribes Epi-pens and teaches families/patients how to use them, this is more than a little disheartening. Both studies found pre-existing asthma to be a signficant risk factor for severe or worse reactions.

So what can we take from these 2 studies.
1. Milk, peanut and tree nut allergy seem to lead to most severe, near-fatal and fatal reactions
2. Avoidance is the best strategy
3. Patients should have Epi-pen available, carry it with them ALWAYS and use it! It does no good if it is sitting at home

There is some contoversy about who exactly needs to carry an Epi-pen, with US docs prescribing them more widely than those in Europe. This study would indicate they are underprescribed there.