This article focuses on the manifestations of childhood food allergy and highlights strategies to help practitioners identify it in primary care. It also covers the most commonly seen food allergies and the initial advice and management required when a diagnosis is made. For further information and resources, particularly in regard to management of food allergy, go to the Irish Food Allergy Network (IFAN) website at www.ifan.ie.
Food hypersensitivity is an umbrella term used to describe adverse reactions to food and includes food allergy, which involves the immune system, and food intolerances, which do not. Food hypersensitivity is a common problem with up to a third of parents describing their child as having an adverse reaction to food at some time during childhood. Food allergy is the largest single cause of food hypersensitivity in childhood and it can be further divided into IgE mediated (immediate) reactions or non-IgE mediated (delayed) reactions. Food allergy is common with recent data from a large birth cohort from Cork reporting an incidence of 4.5% in Irish children with proven immediate food allergy (it is estimated that an additional 1-2% of children have delayed food allergy). This is in keeping with an internationally reported prevalence of food allergy in children of between 5% – 10%.
It is important to distinguish food allergy, especially IgE mediated allergy, from other forms of food hypersensitivity because symptoms are replicated on subsequent exposures to that food and may, albeit rarely, cause severe or life threatening reactions. A clear diagnosis of food allergy allows for the provision of dietary advice, the evaluation of future risks and the prescription of appropriate treatment. It’s important however that unnecessarily restrictive diets which may impact on a child’s growth and quality of life are avoided.
Recognising Food allergy
The diagnosis of food allergy is largely based on a detailed allergy focused history and examination. IgE mediated (immediate) food allergy usually presents as a reaction which may involve the skin, respiratory, circulatory or gastrointestinal systems. Skin manifestations include rashes such as urticaria (hives), angioedema (swelling), erythema (redness) and itch. The rash is particularly noted at the site of contact, usually around the mouth or on the hands, but may become generalised. The presence of airway (hoarseness, cough, stridor, wheeze) or circulatory (syncope, collapse) symptoms indicate a severe or potentially life threatening reaction also known as anaphylaxis.
The timing of the onset of any of these symptoms is a crucial historical feature with immediate reactions occurring, usually within minutes but always (by definition), within 2 hours of exposure. It is important to record how reactions resolve, most food induced reactions resolve within hours, often accelerated by the administration of antihistamine. Urticarial rashes which are noted independent of food exposure (eg on waking) or that last for days are rarely due to food and usually have another cause such as a viral infection. Consistency is also important as true food allergy will always result in a reaction when there is repeated exposure to the same form of the food. For example a parent who is concerned that their child is allergic to milk but who can eat regular dairy ice-cream without difficulty is unlikely to have a milk allergy.
Another key aspect of an allergy focused history is to identify the presence of predisposing factors in particular eczema. The majority of children with food allergy have underlying eczema and the majority of children with severe eczema will have food allergy. Occasionally the eczema will have resolved by the time the child presents and this information will only be available from the history. Milk allergy may present without a history of eczema however it is unusual (though not impossible!) to have egg or peanut allergy without a history of eczema. It is important to stress however that beyond infancy, food rarely causes eczema to flare with most eczema exacerbations reflecting the cyclical nature of the condition.
Non-IgE mediated (delayed) food allergy occurs hours or days after exposure. Whilst there are well defined cell mediated conditions such as eosinophillic proctitis (allergic inflammation of the lower bowel) in infants most non-IgE mediated food allergy is non-specific and is usually considered amongst a long list of alternative diagnoses, especially in young children. A small percentage of common conditions such as infant colic or gastroesophageal reflux are caused by food allergy, in particular cows’ milk protein. Whereas food allergy is only an occasional cause of these conditions it is important to consider, as a trial of elimination and reintroduction may uncover a cure for distressing symptoms.
An allergy focused examination should look for evidence of other allergic conditions such as eczema, asthma or allergic rhinitis. It is very important to assess the child’s nutritional status, noting weight, length and subcutaneous fat stores.
In practice food allergy testing is currently only available for IgE mediated reactions. Confirming a diagnosis of food allergy is important as it justifies the avoidance of the suspect food allergen(s) and the implementation of an appropriate management plan. Conversely, a negative allergy test may allow for safe dietary expansion. IgE to specific allergens may be measured by blood testing (previously called RAST testing) or by skin prick testing (SPT). If considering specific IgE testing it is important to be aware of allergic sensitisation. Only when an individual demonstrates raised IgE to a food allergen (eg peanut) and reacts on contact with allergy symptoms (eg urticaria, angioedema, wheezing) are they considered allergic. Many individuals have a raised specific IgE but will not react on contact with the allergen; these individuals have allergic sensitisation but not allergy. This is important in order to understand allergy testing as to indiscriminately measure specific IgE or SPTs will yield many people who are sensitised but not allergic (ie over-diagnosis), reiterating the importance of the allergy focused history, and examination when choosing tests.
In primary care in Ireland access to allergy testing is essentially limited to blood specific IgE measurement which is sufficient but practitioners need to gain experience requesting and interpreting tests. In general restricting your tests to the food(s) under immediate consideration (for example: egg in a child with an egg reaction) and associated high risk foods (peanut in a child with egg allergy and eczema) is a good strategy. Community dietitians and public health nurses may need to discuss cases with their medical colleagues in General Practice to request such tests. Local paediatric allergy services are happy to guide with advice on testing.
In the case of non-IgE mediated food allergy there is currently no validated, reliable test with the exception of dietary exclusion and reintroduction. Because these reactions are generally mild (although troublesome) it is generally safe to reintroduce foods at home provided there is no evidence of IgE mediate allergy nor a history of a previous severe reaction.
It is important that practitioners have awareness of “alternative” allergy tests available to patients in the community, many of which are expensive. European and American allergy associations have recommended against using Vega testing, kinesiology and hair testing on the basis that there are no studies to support their use. They also advise against using IgG (as opposed to IgE) testing to foods as there is no validated evidence to support its use at this time.
Common Childhood Food Allergies
Cows’ milk, hen’s egg and nuts are responsible for the majority of food-induced allergic reactions in children. Most children with food allergy are allergic to more than one food. In general children with milk or egg allergy are likely to outgrow them during childhood, whilst those with nut or fish allergies are likely to remain allergic into adulthood.
Cows’ Milk Protein Allergy (CMPA): This is the most common food allergy of early childhood as it the main exposure that infants have with cohort studies estimating a rate of around 2.5%. It is well recognised that there is IgE- and non-IgE-mediated CMP allergies and occasionally they are mixed. Whereas IgE-mediated allergy is usually identified easily, non-IgE-mediated allergy can be more difficult to recognise.
IgE-mediated CMPA usually presents obviously after the first exposure to a CMP formula with the infant often having been successfully breastfed for months, however it may present more insidiously in babies who have been formula-fed since birth. Symptoms will only occur on exposure to CMP formula milk or products containing it. Blood specific IgE or SPT will confirm the diagnosis and exclusion of CMP is the mainstay of treatment. There are several alternative formulas available for those allergic to cows’ milk – see below.
Non-IgE-mediated CMPA is less specific and is harder to diagnose. As discussed above it can cause common conditions of infancy such as constipation, infant colic and GOR. The main test for this is the withdrawal and reintroduction of milk at home, unless there are concerns about IgE-mediated disease.
Breast milk is the preferred feed for all infants, and rarely, an infant may react to the very small amounts of CMP secreted intact into human breast milk. A trial of excluding CMP from a mother’s diet should only be recommended by a paediatrician and undertaken with dietitian supervision.
Standard infant formula contains unadulterated CMP, which can be broken down by hydrolysation into small fragments which are less recognisable to the immune system. Extensively hydrolysed formula (EHF) and amino acid formula (AAF) are used for confirmed CMP allergy. Partially hydrolysed formula should not be given to children with CMP allergy. Most babies with CMP allergy will tolerate EHF and this is a reasonable product to start with. Babies who have not tolerated EHF or who had an initial severe reaction may require an AAF. Hydrolysed formulae are recommended for any baby under six months. Soy-based formulae may be used for babies over six months, but are avoided in babies with CMP allergy less than six months because of the possibility of developing soy allergy. Sheep and goat milk are not recommended due to high cross-reactivity and poor nutritional composition. Plant-based milks (oat, pea, almond milk, etc) are not recommended because they will not meet nutritional requirements in children under two. Rice milk is not recommended in children less than five years because of concerns regarding arsenic levels.
As delayed milk allergy resolves baked milk products may be used to promote tolerance. This needs to be under medical or dietitian supervision. For more information we recommend readers visit the excellent Milk Allergy in Primary Care (MAP) website at www.cowsmilkallergyguidelines.co.uk.
Egg allergy is the most common childhood allergy (3% of children in the Cork cohort). Raw or lightly cooked egg (scrambled egg, omelette, mayonnaise, meringues) is most allergenic with baked egg (buns, cake) less so. Eating baked egg seems to accelerate the resolution of allergy to lightly cooked egg but an assessment is required to know when this is safe to do. See the Egg Ladder at www.ifan.ie for more.
It is important to stress that the MMR vaccine does not contain egg and that children with egg allergy should be vaccinated in the community the same as everyone else. Influenza and yellow fever vaccines may contain egg proteins and should be discussed with a doctor before administration.
Nut allergy affected 1.8% of children in the Cork cohort. Peanut – a ground nut – is the most common cause of nut allergy. The most common tree nut allergies are hazelnut and cashew nut. There are some cross-reactivities between tree nuts (cashew with pistachio and walnut with pecan). Nuts can provoke more severe reactions than other foods and therefore adrenaline is prescribed even if previous reactions were mild. Nut avoidance can be difficult as they are ingredients in many foods (and therefore should be listed on the label) but even when they are not labels may have cautionary warnings such ‘may contain traces of nuts’. While efforts are afoot to improve labelling, parents should be encouraged to avoid foods with such warnings. This cautious approach can be summed up as ‘No label, no eat. No adrenaline, no eat’. Most children with nut allergies do not outgrow them, however they will need assessment to see if they are among the many or the few.
Management of Diagnosed Food Allergy
Once a diagnosis of food allergy is confirmed then a management plan should be recommended to the child and family. An important feature of this plan is a risk assessment as to the likelihood of a severe reaction or anaphylaxis occurring.
In our experience children and families benefit from a written allergy plan which can be shared with school. The plan should name the food which the child is avoiding and clearly define the features of a (mild to moderate or severe) reaction and the appropriate action needed in response. Sample plans are available on the IFAN website.
In one sense the management of food allergy is simple in that the implicated food should be excluded from the diet. In the case of non-IgE mediated allergy this may be for a period of 4-6 weeks before reintroduction to see if symptoms recur. In the case of IgE mediated allergy, once confirmed the food is usually excluded for longer periods until such time as further testing suggests that it is safe to reintroduce the food. For most foods this will mean a formal food challenge in hospital although in certain cases (eg. baked egg) this could be undertaken at home once a thorough risk assessment has occurred to ensure this would be safe to do.
In reality, avoiding common foods (eg milk, egg, nuts) is difficult as they are often ingredients in other food stuffs. Educating parents and families in this regard and ensuring they can read food labels is an essential component of management. Printed information is available for the dietary management of many food allergies (IFAN or BSACI). Dietitian input is always helpful and is essential for children with multiple food allergies where there are difficulties finding suitable foods or whenever there are concerns about faltering growth.
Medication – Adrenaline & Antihistamines
Although avoidance is the cornerstone of treatment, many children will have accidental exposures to the food to which they are allergic to and some will react to new foods. The most commonly used medication to treat allergic reactions are antihistamines. A non-sedating antihistamine should be easily accessible to all children with known food allergy for the management of mild to moderate reactions.
The management of severe allergic or anaphylactic reactions requires intramuscular adrenaline as the first line treatment. Other medications such as oxygen, bronchodilators and antihistamines may also be required once the adrenaline is administered (or whilst waiting for it). There are international guidelines as to who requires an adrenaline autoinjector (Table 1). Although included amongst the relative indications it is our practise to recommend adrenaline to children with a confirmed nut allergy.
It is advisable that two devices are with the child at all times because in a quarter of cases where adrenaline is given a second dose may be required. If adrenaline is prescribed then it is incumbent upon the prescriber that the indications for use and how to use it are clearly explained and demonstrated.
A major risk factor for having a severe or even fatal food allergic reaction is the presence of asthma especially if poorly controlled. Special attention must be given to children with co-existing food allergy and asthma and they must have their asthma treatment stepped up until it is well controlled.
|Who requires an adrenaline autoinjector?|
• Previous cardiovascular or respiratory reaction (ie anaphylaxis) to a food, insect sting or latex.
• Exercise induced anaphylaxis.
• Idiopathic anaphylaxis.
• Child with food allergy and co-existent persistent asthma.
• Any reaction to small amounts of a food (e.g. airborne food allergen or contact only via skin).
• History of only a previous mild reaction to peanut or a tree nut.
• Remoteness of home from medical facilities.
• Food allergic reaction in a teenager.
Table 1: Recommendations from European academy of allergology and clinical immunology (EAACI) on prescription of adrenaline.
Atopy (eczema, food allergy, rhinoconjunctivitis and asthma) is the most common chronic disease of childhood. Food allergy is on the increase and is an important cause of concern for children and families that needs greater recognition.
There is good evidence now that seeing a paediatrician with experience in managing allergic disease improves patient outcomes and reduces the risk of severe reactions. In addition children with previously confirmed IgE mediated allergy need assessment to see if a food challenge is required so as to cease unnecessary elimination diets. It is important that this is recognised at a national level to make provision for these children and their families in primary and secondary care. This will include supporting allergy training for paediatricians, GPs, dietitians and nurses and expanding the current roles of some of these groups. We will need to change how we work together in order to meet the demands of the years ahead and to provide the services our children and young people deserve into the future.
Irish Food Allergy Network (IFAN) is a collaboration of health professionals interested in advancing the quality of paediatric food allergy in Ireland.
References available on request
Lactose intolerance is commonly confused with CMPA.
Lactose intolerance is due to an inability to digest lactose. There are three major types of lactose intolerance in infancy: congenital, primary and secondary.
Congenital absence of intestinal lactase is rare but severe, and presents in the neonatal period with loose stools from initial exposure to either human or formula milk, both of which contains lactose. There is subsequent faltering growth and lifelong symptoms if a diet excluding lactose is not followed.
Primary lactase deficiency (hypolactasia) is a relatively common condition caused by a deregulation of the lactase gene expression, which may occur in up to 4% of the Irish population. In the majority of these patients however, symptoms may not develop until late childhood or adulthood.
Secondary lactose intolerance refers to those infants who have previously tolerated lactose-containing feeds, however lose lactase enzyme activity secondary to inflammatory or structural damage to the small intestinal mucosa, like that caused by gastroenteritis. This is transient and usually resolves within a few weeks. Avoidance is not necessary unless the child is particularly symptomatic.
The symptoms of lactose intolerance include abdominal cramps, excessive flatus, explosive loose stools, abdominal distension and perianal excoriation due to an increased lactic acid concentration in stools. In infancy, the diagnosis is usually made by trial on lactose elimination diet followed by re-challenge and therefore invasive testing is rarely needed. There are several lactose-free infant formulas available including those based on whole CMP, EHF, AAF or soy.
Prevention of Food Allergy in Children
Recent research has highlighted the influence of early (from the age of 3-4 months) exposure to foods on the acquisition of tolerance (ie the opposite to allergy). Two studies, the LEAP and the EAT studies have shown the tolerance benefit of early introduction of complimentary foods associated with allergy (eg peanut in the LEAP study, while continuing to breast or bottle feed) in children at risk of developing food allergy. In children with risk factors such as eczema or a pre-existing food allergy this should be under advice from a healthcare professional.