Lactose (and other disaccharide) intolerance is a common secondary event after infection, with coeliac disease, food allergic enteropathy and inflammatory bowel disease. The duration is variable.

Important features from history

Personal history of atopic disease: asthma, eczema or hayfever
Family history of atopic disease or food allergy
Details of foods that are avoided and the reasons why
Specific questions:
- Age of the child or young person when symptoms first started?
- Speed of onset of symptoms following food contact?
- Duration of symptoms?
- Severity of reaction
- Frequency of occurrence
- Setting of reaction, e.g. at school or home?
- Reproducibility of symptoms on repeated exposure?
- What food and how much exposure to it causes a reaction?
- Who has raised the concern and suspects the food allergy?
- What the suspected allergen is?
Cultural and religious factors that affect the foods eaten
Child or young person’s feeding history: breast-fed or formula-fed, the age at which they were weaned – if the child is currently being breast-fed, consider the mother’s diet
Details of any previous treatment, including medication; any response to the elimination and re-introduction of foods

Information: Common food allergy triggers

Cow’s milk
Soya bean (a legume)
Egg
Wheat
Fish
Shellfish
Peanut
Tree nuts, e.g. hazel, almond, pistachio

Investigations

The gold-standard test is the double-blind placebo-controlled cross-over food challenge, which is technically difficult and time-consuming. In practice, open food challenges are used.

Allergy sensitisation tests:
- IgE-mediated allergy: RAST or skin prick testing for suspected triggers
- Non-IgE-mediated allergy: patch tests
- Results are difficult to interpret, because of false-negatives and non-specific sensitisation.
Lactose, fructose or sucrose breath tests: small bowel or colonic intestinal bacteria ferment undigested sugars, producing hydrogen. A rise in hydrogen detected in exhaled breath is suggestive of a sugar malabsorption, especially when supported by a 48-hour symptom diary
Evaluate further for non-allergic gastrointestinal disease if faltering growth and/or severe gastrointestinal symptoms have not responded to a single-allergen elimination diet; see Chapters 6, 9 and 10

Information: Cow’s milk allergic colitis

Presents with bright red blood streaks in stools
Rarely hypoproteinaemia and oedema
Typically endoscopy shows colonic lymphoid nodular hyperplasia
Biopsies may show an eosinophilic inflammatory infiltrate
Food protein-induced enteropathy syndrome (FPIES): a severe form can be mistaken for necrotising enterocolitis