27 research outputs found
Non-IgE-mediated food allergies
Non-imunoglobulin E (IgE)-mediated conditions include combined IgE and cell-mediated conditions such as atopic dermatitis and eosinophilic oesophagitis, and pure T-cell-mediated conditions such as food protein-induced enterocolitis syndrome, allergic proctocolitis and enteropathy syndromes. Diagnosing mixed or non-IgE-mediated allergy is challenging. A clear cause-effect relationship between exposure to the suspected food and symptoms is not always possible, as symptoms develop over time and are more chronic in nature. Skin-prick tests and specific IgE to the allergen are usually negative. An elimination diet may be necessary to diagnose non-IgE-mediated type food allergy. The suspected allergen should be excluded from the diet for 2 - 6 weeks under dietetic guidance to assess for improvement of symptoms. After symptom improvement, a rechallenge is necessary to definitively prove causal relation.
Severe food allergy and anaphylaxis : treatment, risk assessment and risk reduction
An anaphylactic reaction may be fatal if not recognised and managed appropriately with rapid treatment. Key steps in the management of
anaphylaxis include eliminating additional exposure to the allergen, basic life-support measures and prompt intramuscular administration
of adrenaline 0.01 mg/kg (maximum 0.5 mL). Adjunctive measures include nebulised bronchodilators for lower-airway obstruction,
nebulised adrenaline for stridor, antihistamines and corticosteroids. Patients with an anaphylactic reaction should be admitted to a medical
facility so that possible biphasic reactions may be observed and risk-reduction strategies initiated or reviewed after recovery from the acute
episode.
Factors associated with increased risk of severe reactions include co-existing asthma (and poor asthma control), previous severe
reactions, delayed administration of adrenaline, adolescents and young adults, reaction to trace amounts of foods, use of non-selective
β-blockers and patients who live far from medical care.
Risk-reduction measures include providing education with regard to food allergy and a written emergency treatment plan on allergen
avoidance, early symptom recognition and appropriate emergency treatment. Risk assessment allows stratification with provision of
injectable adrenaline (preferably via an auto-injector) if necessary. Patients with ambulatory adrenaline should be provided with written
instructions regarding the indications for and method of administration of this drug and trained in its administration. Patients and their
caregivers should be instructed about how to avoid foods to which the former are allergic and provided with alternatives. Permission must
be given to inform all relevant caregivers of the diagnosis of food allergy. The patient must always wear a MedicAlert necklace or bracelet
and be encouraged to join an appropriate patient support organisation.http://www.samj.org.zahb201
Vaccination in food allergic patients
Important potential food allergens in vaccines include egg and gelatin. Rare cases of reactions to yeast, lactose and casein have been reported.
It is strongly recommended that when vaccines are being administered resuscitation equipment must be available to manage potential
anaphylactic reactions, and that all patients receiving a vaccine are observed for a sufficient period.
Children who are allergic to egg may safely receive the measles-mumps-rubella (MMR) vaccine; it may also be given routinely in primary
healthcare settings. People with egg allergy may receive influenza vaccination routinely; however, some authorities still perform prior skinprick
testing and give two-stage dosing. The purified chick embryo cell culture rabies vaccine contains egg protein, and therefore the human
diploid cell and purified verocell rabies vaccines are preferred in cases of egg allergy.
Yellow fever vaccine has the greatest likelihood of containing amounts of egg protein sufficient to cause an allergic reaction in allergic
individuals. This vaccine should not be routinely administered in egg allergic patients and referral to an allergy specialist is recommended,
as vaccination might be possible after careful evaluation, skin-testing and graded challenge or desensitisation.http://www.samj.org.zahb201
Diagnosis of food allergy : history, examination and in vivo and in vitro tests
One cannot depend on one single test to diagnose food allergy. A detailed history is an essential initial step in cases of suspected food allergy.
Aspects of the history should be gathered separately for each food being considered, as a patient may experience different types of reactions
with various foods, each of which requires individual diagnostic and management strategies. History alone is not diagnostic and additional
measures of sensitisation or food challenges are often required.
In suspected immunoglobulin E (IgE)-mediated allergy, skin-prick tests (SPTs) and/or measurement of serum specific IgE antibodies
(ImmunoCAP) to suspected foods is used to prove sensitisation. Sensitisation does not, however, confirm clinical food allergy as these tests
indicate an immunological response to the specific allergen, but the diagnosis requires a clear correlation between the test result and clinical
reaction (by positive history or food challenge). The magnitude of the test result (SPT mean wheal size or ImmunoCAP level in kU/L)
correlates with the likelihood of clinical allergy, but not the severity of a reaction.
Choice of the allergens tested should be guided by the history, but limited to the lowest necessary number to avoid false-positive results. Tests
for sensitisation to foods should not be performed when the history indicates that such foods are tolerated. Ninety-five per cent positive predictive
values (where a clinical reaction can be predicted in 95% of cases) have been described for immediate reactions, but may be population specific.
There are no validated tests to confirm non-IgE- or mixed IgE- and non-IgE-mediated food allergies. Diagnosis of this group of allergies
depends on elimination of the suspected food, clearance of symptoms, and recurrence of symptoms on re-introduction of the food.http://www.samj.org.zahb201
Epidemiology of IgE-mediated food allergy
Despite the large number of foods that may cause immunoglobulin E (IgE)-mediated reactions, most prevalence studies have focused on
the most common allergenic foods, i.e. cow’s milk, hen’s egg, peanut, tree nut, wheat, soya, fish and shellfish.
Food allergy peaks during the first two years of life, and then diminishes towards late childhood as tolerance to several foods develops.
Based on meta-analyses and large population-based studies, the true prevalence of food allergy varies from 1% to >10%, depending on the
geographical area and age of the patient.
The prevalence of food allergy in South Africa (SA) is currently being studied. The prevalence of IgE-mediated food allergy in SA
children with moderate-to-severe atopic dermatitis is 40%; however, this represents a high-risk population for food allergy. Preliminary data
from the South African Food Sensitisation and Food Allergy (SAFFA) study, which is investigating food allergy in an unselected cohort of
1 - 3-year olds, show a prevalence of 11.6% sensitisation to common foods. Food allergy was most common to egg (1.4%) and peanut (1.1%).
Food allergy appears to be the most common trigger of anaphylactic reactions in the community, especially in children, in whom food is
responsible for ≥85% of such reactions. In adults, shellfish and nut, and in children, peanut, tree nut, milk and egg, are the most common
triggers of food-induced anaphylaxis.http://www.samj.org.zahb201
Exclusion diets and challenges in the diagnosis of food allergy
Instituting an exclusion diet for 2 - 6 weeks, and following it up with a planned and intentional re-introduction of the diet, is important for
the diagnosis of a food allergy when a cause-and-effect relationship between ingestion of food and symptoms is unclear.
Food may be re-introduced after (short-term) exclusion diets for mild-to-moderate non-immunoglobulin E (IgE)-mediated conditions in
a safe clinical environment or cautiously at home. However, patients who have had an IgE-mediated immediate reaction to food, a previous
severe non-IgE-mediated reaction or a long period of food exclusion should not have a home challenge, but rather a formal incremental
food challenge protocol in a controlled setting.
An incremental oral food challenge (OFC) test is the gold standard to diagnose clinical food allergy or demonstrate tolerance. It consists
of gradual feeding of the suspected food under close observation. It should be done by trained practitioners in centres that have experience
in performing the procedure in an appropriate setting.
An OFC must be performed in a setting where resuscitation equipment is available in the event of a severe anaphylactic reaction. OFCs are
terminated when a reaction becomes apparent. Standardised and pre-set criteria are available on when to discontinue challenges. Patients who
tolerate the full dose ‘pass’ the challenge and are advised to eat a full portion of the food at least twice a week to maintain tolerance. Those who
have reactions have ‘failed’ the challenge, should avoid the food, receive education and implement risk-reduction strategies where appropriate.
Patients should be observed for a minimum of 2 hours following a negative challenge and for 4 hours after a positive one.http://www.samj.org.zahb201
Elimination diets and dietary interventions for the management of food allergies
The primary therapy for food allergy is strict avoidance of the offending food or foods. Dietary restriction should be tailored to meet the
nutritional requirements of each patient. Patients should be educated on how to avoid allergens safely by understanding terminology for
common ingredients and how to read food labels. Information regarding safe, cost-effective and freely available substitutes for the avoided
foods should be provided. Patients should be re-evaluated at regular intervals to see if they have developed tolerance.
Mothers of infants with cow’s milk protein allergy (CMPA) who are breastfeeding should be supported and encouraged to continue
breastfeeding. Partially hydrolysed infant formulas are not hypoallergenic (tolerated by 90% of subjects with proven CMPA) and are therefore
not recommended for the treatment of CMPA, but may have a role in prevention of eczema or CMPA in high-risk individuals.
Some extensively hydrolysed and amino-acid-based formulas are truly hypoallergenic. The recommended feed of choice for the dietary
management of mild-to-moderate CMPA in infants not breastfed is an extensively hydrolysed cow’s milk formula. The recommended
formula for the dietary management of non-breastfed infants and children with known severe CMPA is an amino-acid-based formula.
Soya-based formulas may be useful in infants with immunoglobulin E (IgE)-mediated CMPA with proven tolerance to soya, and some cases
of mild-to-moderate non-IgE-mediated CMPA, bearing in mind the increased risk of co-reactivity between CMPA and soya allergy in non-
IgE-mediated conditions. Other mammalian milks and plant-based milks, including rice and oat milks, are not suitable as sole nutrition for
cow’s milk protein allergic individuals.http://www.samj.org.zahb201
Novel therapies in the management of food allergy : oral immunotherapy and anti-IgE
The process of oral immunotherapy (OIT) consists of a series of dose escalations with the immediate goal of inducing desensitisation and
ultimately achieving a state of tolerance.
Owing to the limitations of OIT, including side-effects and lack of proven efficacy in long-term tolerance induction, it is not yet
recommended in routine clinical practice and should be restricted to the research setting.
Studies using anti-immunoglobulin E (IgE) antibody in food allergy management are limited, but show promising results. The possible
applications are for increasing the sensitivity threshold to certain foods such as peanut, and also for use in combination with OIT to enhance
safety and rapidity of the OIT process; however, anti-IgE is not yet licensed for use in food allergy.http://www.samj.org.zahb201