Food Poisoning and Food Allergy

What to remember

• Food poisoning is an illness caused by eating food contaminated with germs, their toxins, chemicals or natural poisons; the common signs are vomiting, abdominal pain and diarrhoea.
• Staphylococcus aureus gives quick-onset poisoning (1-6 hours) from a heat-stable toxin; Salmonella is an infection with a longer incubation; Clostridium botulinum gives a deadly nerve toxin in canned foods.
• Food allergy is an immune (IgE) reaction to a food protein, while food intolerance (such as lactose intolerance) is a non-immune enzyme problem.

Food-borne illness: basic ideas

Food-borne illness is a general term for disease caused by contaminated food. It may be:

• Food infection: the germs themselves in the food multiply in the body and cause illness (Salmonella, Shigella, Vibrio cholerae, E. coli).
• Food intoxication: a toxin already made in the food by germs causes the illness; living germs need not be present (Staphylococcus aureus, Clostridium botulinum, Bacillus cereus emetic type).
• Toxin-infection: germs are swallowed in large numbers and then make a toxin in the gut (Clostridium perfringens).

The incubation period is the time from eating the food to the first symptoms. Short incubation points to a pre-formed toxin; longer incubation points to infection.

Sources of contamination: infected food handlers, flies, dirty water, unwashed hands, raw and cooked food mixed, unclean utensils, rats, and food kept in the warm "danger zone" (about 5-60 °C).

Bacterial food poisoning

A bulging or leaking can, or a can with a bad smell, must be thrown away. Home-canned foods should be boiled for about 10 minutes before eating.

Chemical, plant and fungal food poisoning

Chemical contamination

• Pesticide residues on vegetables and fruits, and misused food colours.
• Heavy metals: arsenic, lead (from lead-glazed utensils), cadmium (itai-itai disease), mercury (Minamata disease, from contaminated fish).
• Food stored in unglazed or copper vessels may cause metal poisoning.

Natural plant toxins and diseases

Goitrogens (in cabbage, cauliflower, and some millets and cassava) interfere with iodine use by the thyroid and are harmless when iodine intake is enough.

Adulteration examples: metanil yellow in turmeric and sweets; argemone oil in mustard oil; khesari dal in arhar dal; chalk powder in flour; water in milk.

Symptoms, first aid and treatment

Common symptoms: nausea, vomiting, stomach pain, diarrhoea, fever, weakness and sometimes dehydration. In serious cases (botulism, mushroom poisoning) there may be paralysis or loss of consciousness.

• Give plenty of fluids; oral rehydration solution (ORS) to replace water and salts.
• Avoid anti-diarrhoeal drugs without advice. Give a light diet.
• Go to a doctor at once if there is blood in stools, high fever, signs of dehydration, nerve symptoms, or if the patient is an infant, a pregnant woman or an elderly person.
• Keep a sample of the suspected food for tests; inform the health authority if several people are sick.

Prevention of food poisoning

The WHO "Five Keys to Safer Food" are: keep clean; separate raw and cooked; cook thoroughly; keep food at safe temperatures; use safe water and raw materials.

• Wash hands with soap before cooking and eating and after using the toilet.
• Cover cuts and wounds; food handlers with infections or diarrhoea must not cook.
• Cook meat, poultry and eggs well. Cool cooked foods quickly and keep them either hot (above 60 °C) or cold (below 5 °C).
• Reheat leftovers until steaming hot, once only.
• Control flies, rats and cockroaches; keep the kitchen clean and refuse covered.
• Use clean, boiled or chlorinated water; wash vegetables.
• Do not use damaged cans; check dates on packed foods.
• Store grains dry to avoid fungal growth; discard mouldy nuts and grains.
• Anganwadi centres serving cooked meals should follow strict hygiene because the children are very vulnerable.

Food allergy and intolerance

Food allergy is an abnormal immune response to a food protein (the allergen). The body makes IgE antibodies, and on later exposure histamine and other chemicals are released.

• Common allergenic foods: cow's milk, egg, peanut, tree nuts, soy, wheat, fish and shellfish. These are often called the major food allergens.
• Symptoms: itching, hives (urticaria), swelling of lips and face, rash or eczema, vomiting, diarrhoea, wheezing, running nose; the severe form is anaphylaxis with fall in blood pressure and breathing trouble. Anaphylaxis is a medical emergency treated with adrenaline (epinephrine) injection.
• Diagnosis: careful food history, skin prick test, blood tests for IgE, and an elimination diet followed by controlled challenge.
• Management: avoid the allergen completely; read food labels; give a nutritionally adequate substitute diet; infants with cow's milk allergy may need a special hydrolysed formula; exclusive breastfeeding for the first six months lowers the risk. Many children outgrow milk and egg allergy, but peanut and shellfish allergy often continue.

Food intolerance does not involve the immune system.

Food additives such as tartrazine (yellow dye), sulphites and monosodium glutamate may cause reactions in some people.

Comparison: allergy vs intolerance

Exam traps

• Staphylococcus gives quick (1-6 hour) poisoning from a heat-stable toxin; Salmonella is a longer-incubation infection.
• Botulinum toxin is destroyed by boiling, but the spores survive; Staphylococcus toxin is not destroyed by boiling.
• Lathyrism is from khesari dal; epidemic dropsy is from argemone oil in mustard oil; aflatoxin is from fungus on groundnut.
• Cabbage-type foods are goitrogens, not toxins of the liver.
• Lactose intolerance is not an allergy; it is an enzyme deficiency.
• Coeliac disease needs a gluten-free diet; wheat, barley and rye are avoided but rice and maize are not.
• Allergy involves IgE and the immune system; intolerance does not.
• Adrenaline, not antibiotics, is the first emergency drug for anaphylaxis.

One-liners

• 1. Staphylococcus aureus toxin is heat stable.
• 2. Clostridium botulinum is an anaerobe found in badly canned food.
• 3. Salmonella is commonly linked to poultry and eggs.
• 4. Bacillus cereus is linked to cooked rice left at room temperature.
• 5. Lathyrism causes paralysis of the legs.
• 6. Argemone oil causes epidemic dropsy.
• 7. Aflatoxin comes from Aspergillus flavus.
• 8. Ergot is a fungus of rye and bajra.
• 9. Anaphylaxis is treated with adrenaline.
• 10. Lactase breaks down lactose.
• 11. Gluten is found in wheat, barley and rye.
• 12. ORS is the first treatment to prevent dehydration.

Practice questions

1. Food poisoning from a pre-formed, heat-stable toxin with quick onset (1-6 hours) is typical of

   1. Vibrio cholerae
   2. Shigella
   3. Salmonella
   4. Staphylococcus aureus
   Answer

   D. Staphylococcus aureus

   Staph enterotoxin is heat stable and causes vomiting within hours.

2. Botulism is caused by

   1. Bacillus cereus
   2. Listeria monocytogenes
   3. Escherichia coli
   4. Clostridium botulinum
   Answer

   D. Clostridium botulinum

   It makes a nerve toxin in badly canned food.

3. Clostridium botulinum grows best in

   1. Acidic fruit juices
   2. Boiling water
   3. Strong sunlight
   4. Absence of oxygen
   Answer

   D. Absence of oxygen

   It is an anaerobe found in low-acid canned foods.

4. The toxin of Clostridium botulinum is destroyed by

   1. Freezing
   2. Boiling for about 10 minutes
   3. Adding salt only
   4. Refrigeration
   Answer

   B. Boiling for about 10 minutes

   The toxin is heat labile, though spores are heat resistant.

5. Which food poisoning organism is commonly linked with poultry and eggs?

   1. Aspergillus flavus
   2. Clostridium botulinum
   3. Salmonella
   4. Staphylococcus aureus
   Answer

   C. Salmonella

   Salmonella is common in poultry, eggs and meat.

6. Food poisoning linked to cooked rice left at room temperature is caused by

   1. Bacillus cereus
   2. Vibrio cholerae
   3. Campylobacter
   4. Clostridium botulinum
   Answer

   A. Bacillus cereus

   Its spores survive cooking and germinate on standing.

7. Lathyrism is caused by excess consumption of

   1. Bengal gram
   2. Soybean
   3. Green gram
   4. Khesari dal (Lathyrus sativus)
   Answer

   D. Khesari dal (Lathyrus sativus)

   The neurotoxin β-ODAP causes spastic paralysis of the legs.

8. Epidemic dropsy is due to adulteration of mustard oil with

   1. Argemone oil
   2. Groundnut oil
   3. Palm oil
   4. Castor oil
   Answer

   A. Argemone oil

   The toxin is sanguinarine.

9. Aflatoxin is produced by

   1. Claviceps purpurea
   2. Penicillium only on cheese
   3. Aspergillus flavus
   4. Rhizopus on bread only
   Answer

   C. Aspergillus flavus

   It grows on stored groundnut and grains and damages the liver.

10. Ergotism is caused by a fungus growing on

    1. Potato
    2. Groundnut
    3. Fish
    4. Rye and bajra
    Answer

    D. Rye and bajra

    The fungus is Claviceps purpurea.

11. Itai-itai disease is caused by poisoning with

    1. Arsenic
    2. Mercury
    3. Cadmium
    4. Zinc
    Answer

    C. Cadmium

    Minamata disease is mercury; itai-itai is cadmium.

12. Minamata disease is due to contamination of fish with

    1. Mercury
    2. Lead
    3. Cadmium
    4. Copper
    Answer

    A. Mercury

    Mercury from industrial waste accumulated in fish.

13. Favism occurs in people with deficiency of the enzyme

    1. Lipase
    2. Amylase
    3. Lactase
    4. G6PD
    Answer

    D. G6PD

    Broad beans can cause haemolysis in G6PD deficiency.

14. The sugar milk lactose is not digested in lactose intolerance because of lack of

    1. Sucrase
    2. Lactase
    3. Pepsin
    4. Maltase
    Answer

    B. Lactase

    Lactase splits lactose.

15. Gluten is found in

    1. Egg and fish
    2. Rice, maize and ragi
    3. Milk and curd
    4. Wheat, barley and rye
    Answer

    D. Wheat, barley and rye

    Coeliac disease needs a gluten-free diet.

16. The first-line emergency drug in anaphylaxis is

    1. Adrenaline
    2. Oral glucose
    3. Paracetamol
    4. An antibiotic
    Answer

    A. Adrenaline

    Adrenaline reverses airway swelling and low blood pressure.

17. Antibody involved in typical food allergy is

    1. IgA of breast milk
    2. IgM only
    3. IgE
    4. IgG only
    Answer

    C. IgE

    IgE binds mast cells and releases histamine.

18. Which treatment prevents dehydration in food poisoning with diarrhoea?

    1. Plain sugar water only
    2. Strong tea
    3. Cold fizzy drinks
    4. Oral rehydration solution
    Answer

    D. Oral rehydration solution

    ORS replaces water and salts.

19. Which is the commonest cause of food contamination in a kitchen?

    1. Cooking with a lid
    2. Unwashed hands of the food handler
    3. Sunlight in the kitchen
    4. Using steel vessels
    Answer

    B. Unwashed hands of the food handler

    Hand hygiene is vital for food safety.

20. A swollen, bulging tin of food should be

    1. Boiled for a minute and eaten
    2. Discarded
    3. Used for children only
    4. Stored for a week
    Answer

    B. Discarded

    Bulging indicates gas from spoilage organisms such as C. botulinum.

21. Which of these is a phenylalanine-related inborn error needing a special diet?

    1. Goitre
    2. Kwashiorkor
    3. Phenylketonuria
    4. Beriberi
    Answer

    C. Phenylketonuria

    PKU needs a low-phenylalanine diet.

22. Which food adulterant is added to turmeric to give a yellow colour?

    1. Metanil yellow
    2. Khesari flour
    3. Chalk powder
    4. Argemone
    Answer

    A. Metanil yellow

    Metanil yellow is a banned dye.

23. In which condition must a person avoid milk and lactose completely, even in small amounts, from birth?

    1. Anaemia
    2. Scurvy
    3. Galactosaemia
    4. Rickets
    Answer

    C. Galactosaemia

    The infant cannot use galactose, one product of lactose digestion.

24. A canteen worker with a septic boil on the hand prepares custard that causes vomiting 3 hours after eating. The likely cause is

    1. Staphylococcus aureus toxin
    2. Lathyrus toxin
    3. Salmonella infection
    4. Aflatoxin
    Answer

    A. Staphylococcus aureus toxin

    Short incubation and skin infection of the handler point to Staphylococcus.

25. A family develops fever and diarrhoea 24 hours after eating undercooked chicken. The most likely organism is

    1. Staphylococcus aureus
    2. Clostridium botulinum
    3. Aspergillus flavus
    4. Salmonella
    Answer

    D. Salmonella

    Longer incubation with fever suggests infection by Salmonella.

26. A child develops hives and swollen lips within minutes of eating peanuts. This is best called

    1. Kwashiorkor
    2. Food allergy
    3. Food infection
    4. Lactose intolerance
    Answer

    B. Food allergy

    Rapid immune reaction to a food protein.

27. A man has gas and loose stools after drinking milk but no rash or swelling. This suggests

    1. Lactose intolerance
    2. Peanut allergy
    3. Anaphylaxis
    4. Coeliac disease only
    Answer

    A. Lactose intolerance

    Lack of lactase causes non-immune symptoms.

28. Cassava (tapioca) can be harmful if eaten raw or poorly processed because it contains

    1. Solanine
    2. Aflatoxin
    3. Cyanogenic glycosides
    4. Sanguinarine
    Answer

    C. Cyanogenic glycosides

    These release cyanide; proper soaking and cooking remove them.

29. Green or sprouted potatoes contain a toxic substance called

    1. Avidin
    2. Solanine
    3. Gossypol
    4. Ergotamine
    Answer

    B. Solanine

    Solanine causes headache and vomiting.

30. Goitrogens in cabbage and cassava interfere with the use of

    1. Vitamin K
    2. Iron
    3. Calcium
    4. Iodine
    Answer

    D. Iodine

    They block iodine uptake by the thyroid.

31. The WHO 'Five Keys to Safer Food' include

    1. Always fry food twice
    2. Separate raw and cooked foods
    3. Add preservatives to all foods
    4. Store food in the sun
    Answer

    B. Separate raw and cooked foods

    Keep clean; separate raw and cooked; cook thoroughly; safe temperatures; safe water.

32. Which of the following statements is/are correct? 1. Staphylococcal toxin is destroyed by boiling. 2. Botulinum toxin is destroyed by boiling for about 10 minutes.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Staph toxin is heat stable; botulinum toxin is heat labile.

33. Which of the following statements is/are correct? 1. Lactose intolerance is an immune-mediated allergy to milk protein. 2. Food allergy involves the immune system.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Lactose intolerance is an enzyme deficiency, not immune.

34. Which of the following statements is/are correct? 1. Coeliac disease requires a lifelong gluten-free diet. 2. Rice and maize contain gluten.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Rice and maize are gluten-free.

35. Which of the following statements is/are correct? 1. Aflatoxin is a liver carcinogen. 2. Aflatoxin is formed by the fungus Aspergillus flavus.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both statements are correct.

36. Which of the following statements is/are correct? 1. Lathyrism causes weakness and spastic paralysis of the legs. 2. Lathyrism is caused by a deficiency of niacin.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    It is a toxic effect of β-ODAP, not a deficiency.

37. Which of the following statements is/are correct? 1. Salmonella is a pre-formed toxin type of poisoning. 2. Salmonella food poisoning has a longer incubation than staphylococcal poisoning.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Salmonella is an infection type.

38. Which of the following statements is/are correct? 1. Cooked food should be kept either above 60 °C or below 5 °C. 2. Reheated food can be stored and reheated many times safely.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Reheat only once.

39. Which of the following statements is/are correct? 1. Rice is the most common food allergen in infants. 2. Common food allergens include milk, egg and peanut.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Rice is rarely allergenic.

40. Which of the following statements is/are correct? 1. Clostridium perfringens can survive cooking as spores. 2. Bacillus cereus spores can survive cooking.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both form heat-resistant spores.

41. Which of the following statements is/are correct? 1. Peanut allergy is always outgrown by school age. 2. Exclusive breastfeeding for six months helps lower the risk of food allergy.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Peanut allergy often persists.

42. Which of the following statements is/are correct? 1. Epidemic dropsy is caused by argemone seed oil. 2. Epidemic dropsy is caused by aflatoxin.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    The toxin is sanguinarine.

43. Which of the following statements is/are correct? 1. Cadmium causes itai-itai disease. 2. Mercury causes Minamata disease.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both correct.

44. Which of the following statements is/are correct? 1. Washing hands with soap prevents food contamination. 2. Cooked and raw foods may be stored together without covering.

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    They should be kept apart.

45. Which organism, found in soft cheese and raw milk, is especially dangerous in pregnancy and can grow at refrigerator temperature?

    1. Staphylococcus aureus
    2. Vibrio cholerae
    3. Clostridium botulinum
    4. Listeria monocytogenes
    Answer

    D. Listeria monocytogenes

    Listeria can grow in the cold and may harm the fetus.