Food allergy (including cow’s milk protein allergy)

This chapter provides an overview of food allergy and is set out as follows:

Types of reaction

• Most food allergy results in a type I immediate hypersensitivity reaction
• Occasionally food allergy can cause a type IV delayed hypersensitivity reaction  

Foods causing type I reactions

• Egg white, nuts (especially peanuts and tree nuts) and cows milk account for 75% of reactions
• Fish / shellfish (eg cod and prawns), soya, wheat and sesame seeds account for most of the rest
• Fruit and vegetables are less common causes

In the majority of cases investigations are not needed

• Most children with mild-moderate eczema that respond well to treatment do not have a food allergy. In such patients, and in the absence of any close temporal link between a particular food causing a flare of eczema, investigations and dietary restrictions are not recommended
• Irrespective of the clinical context, if there appears to be a close temporal link between a food and the symptoms the diagnosis can be confirmed by dietary exclusion, often without the need for any investigations 

Where the clinical presentation suggests that food allergy is possible but there is uncertainty as to the food involved, total IgE levels and food specific IgE levels (RASTs) may be of use and are measured by way of a blood test, however, RASTs have their limitations

• It needs to be specified on the pathology form as to which foods need to be tested for. If there are no clues from the history it may be necessary to screen for the more common allergens such as cow's milk, egg white, nuts (including tree nuts), fish / shellfish, soya and wheat - it can be helpful to find out from your local pathology laboratory as to what their general RAST screen consists of
• Results of RASTs can be affected by concurrent treatment with antihistamines
• There are many false positive results - a positive RAST only confirms the presence of atopy or sensitivity to a given food, only in some cases does this translate into reactivity and allergy. Indeed, adults with atopic eczema may have high total IgE levels, which in turn may result in multiple false positive RASTs
• RASTs only detect type I reactions and not type IV reactions, which can sometimes be responsible for cow's milk protein allergy 

• Prevention - in infants and very young children there is some evidence that washing hands before applying emollients may reduce the risk of peanut and various other allergies 

• In general, suspect foods (based on history and / or investigations) should be omitted from the diet for four to six weeks. Dietary exclusion should only continue if significant clinical improvements are noted
   
• In terms of the Oral Allergy syndrome, cooking the food as opposed to eating it raw may overcome the problem
   
• Suspected cow's milk protein allergy
  • Exclude cow's milk for four to six weeks
    • In breast feed infants the mother needs to avoid all sources of cow's milk
    • If bottle-fed, replace with a cow's milk and soya free product, some children allergic to cow's milk will also be allergic to soya as a result of a high antigenic cross over. For moderate-severe cases an amino acid-based formula will be needed eg Nutramigen AA or Neocate. For milder cases consider an extensively hydrolysed formula (EHF) eg Nutramigen 1 or 2, which may be more palatable, or if not tolerated consider a whey based formula eg Milupa  
  • If a significant improvement is noted remain off cow's milk and refer to a paediatric dietician. More severe cases may also need paediatric input 
     
• The following patients should be referred to a specialist
  • Certain food allergies - patients with moderate-severe reactions to eggs, or patients with nut allergies as they often have multiple allergies and may require further investigations. Refer to an immunologist or a paediatrician with a special interest in food allergy (refer to local guidelines)
  • Consider referring patients who have severe angioedema / anaphylaxis - refer to the related chapter above on Urticaria: acute urticaria for more information 
     
• Prognosis
  • Patients with allergies to egg, soya and wheat are likely to outgrow their symptoms at a young age
  • With regards to cow's milk protein allergy, while some patients outgrow the allergy at a young age, a recent study has suggested that others, especially with very high levels of specific IgE, are likely to have persistent milk allergy for many years 
  • Patients with allergies to peanut, tree nuts, fish and shellfish are unlikely to outgrow their symptoms
  • High IgE levels may imply a worse prognosis. Specialists monitor IgE levels to assess when it is safe to give patients a food challenge ie it is safer to try a food challenge at lower IgE levels