Food Poisoning

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Introduction

  1. Food poisoning is an acute gastrointestinal illness caused by ingestion of contaminated food or water.

  2. It may be due to:

    • Microorganisms

    • Microbial toxins

    • Chemicals

    • Natural toxins

  3. It is a major public health problem worldwide.

  4. Common in developing countries due to:

    • Poor sanitation

    • Improper food handling

    • Inadequate refrigeration

 

Definition

Food poisoning is defined as:

An acute illness resulting from ingestion of food contaminated with pathogenic microorganisms, their toxins, or harmful chemicals.

Classification of Food Poisoning

A. Based on Mechanism

1. Food Infection

  • Caused by ingestion of live microorganisms

  • Organism multiplies in intestine

  • Produces disease

Examples:

  • Salmonella enterica

  • Escherichia coli

2. Food Intoxication

  • Caused by ingestion of preformed toxin

  • Organism may not be present

  • Rapid onset

Example:

  • Staphylococcus aureus

3. Toxin-Mediated Infection

  • Organism ingested

  • Produces toxin inside intestine

Example:

  • Clostridium perfringens

B. Based on Etiological Agent

  1. Bacterial

  2. Viral

  3. Parasitic

  4. Chemical

  5. Natural toxin

 

Etiological Agents

A. Bacterial Causes

1. Salmonella enterica

  • Source: Poultry, eggs, meat

  • Incubation: 6–48 hours

  • Pathogenesis: Invades intestinal mucosa

  • Symptoms:

    • Fever

    • Diarrhea

    • Abdominal cramps

  • Complication: Septicemia

2. Staphylococcus aureus

  • Gram-positive cocci

  • Produces heat-stable enterotoxin

  • Source: Cream pastries, milk products

  • Incubation: 1–6 hours

  • Severe vomiting prominent

3. Clostridium perfringens

  • Gram-positive bacilli

  • Spore-forming anaerobe

  • Source: Improperly stored meat

  • Incubation: 8–16 hours

  • Causes abdominal cramps

4. Vibrio cholerae

  • Comma-shaped Gram-negative bacillus

  • Produces cholera toxin

  • Rice water stool

  • Severe dehydration

5. Escherichia coli (EHEC)

  • Source: Undercooked beef

  • Bloody diarrhea

  • Complication: Hemolytic uremic syndrome (HUS)

B. Viral Causes

1. Norovirus

  • Most common viral cause

  • Outbreaks in hostels, cruise ships

  • Highly contagious

2. Hepatitis A virus

  • Contaminated water

  • Causes jaundice

  • Incubation: 2–6 weeks

C. Parasitic Causes

  • Entamoeba histolytica

  • Giardia lamblia

 

Pathogenesis

  1. Ingestion of contaminated food.

  2. Survival through gastric acid.

  3. Adherence to intestinal mucosa.

  4. Multiplication.

  5. Toxin production.

  6. Increased intestinal secretion.

  7. Diarrhea and dehydration.

 

Clinical Features

A. Gastrointestinal

  1. Nausea

  2. Vomiting

  3. Watery diarrhea

  4. Bloody diarrhea

  5. Abdominal cramps

B. Systemic

  1. Fever

  2. Headache

  3. Weakness

  4. Dehydration

C. Severe Complications

  1. Shock

  2. Renal failure (HUS)

  3. Septicemia

  4. Liver damage

 

Laboratory Diagnosis

Specimen Collection

  1. Fresh stool sample

  2. Vomitus

  3. Blood culture (if fever)

  4. Suspected food sample

Precautions:

  • Collect before antibiotics

  • Use sterile container

  • Transport immediately

Microscopy

  1. Wet mount

  2. Gram staining

  3. Ova and cyst examination

  4. RBC/WBC in stool

Culture Media

Organism Media
Salmonella XLD agar
E. coli MacConkey agar
Vibrio TCBS agar
Staphylococcus Blood agar

Biochemical Tests

  1. TSI test

  2. Indole test

  3. Citrate test

  4. Urease test

  5. Catalase & Coagulase (Staph)

Serological Tests

  • Widal test

  • ELISA for viral antigens

Molecular Diagnosis

  1. PCR

  2. Multiplex PCR panels

  3. Toxin gene detection

 

Treatment

  1. Oral Rehydration Solution (ORS)

  2. IV fluids (severe cases)

  3. Antibiotics (if indicated)

  4. Anti-emetics

  5. Zinc (children)

 

Prevention

  1. Wash hands properly.

  2. Cook food thoroughly.

  3. Avoid street food contamination.

  4. Refrigerate leftovers.

  5. Safe drinking water.

  6. Avoid cross-contamination.

  7. Maintain personal hygiene.

 

Food Poisoning Outbreak Investigation

  1. Confirm diagnosis.

  2. Collect samples.

  3. Culture & identify pathogen.

  4. Epidemiological tracing.

  5. Implement control measures.

  6. Public health reporting.

 

MCQs

1. Food poisoning is most commonly caused by:

A. Chemical exposure
B. Contaminated food and water
C. Genetic mutation
D. Trauma
Answer: B

2. Food intoxication is caused by:

A. Live bacteria
B. Viral replication
C. Preformed toxin
D. Parasites
Answer: C

3. The most common bacterial cause of food infection is:

A. Salmonella enterica
B. Mycobacterium
C. Corynebacterium
D. Bacillus anthracis
Answer: A

4. Rapid onset vomiting within 1–6 hours suggests:

A. Salmonella
B. E. coli
C. Staphylococcus aureus
D. Vibrio
Answer: C

5. TCBS agar is used to isolate:

A. Salmonella
B. Shigella
C. Vibrio cholerae
D. Staphylococcus
Answer: C

6. The incubation period of Salmonella is:

A. 1 hour
B. 6–48 hours
C. 7 days
D. 1 month
Answer: B

7. Food poisoning due to improperly stored meat is commonly caused by:

A. Clostridium perfringens
B. Staphylococcus
C. E. coli
D. Shigella
Answer: A

8. The most common viral cause of food poisoning is:

A. Rotavirus
B. Norovirus
C. Influenza
D. HIV
Answer: B

9. Bloody diarrhea is commonly seen in:

A. Staph infection
B. Viral infection
C. Escherichia coli (EHEC)
D. Clostridium
Answer: C

10. The primary symptom of Staphylococcal food poisoning is:

A. Fever
B. Vomiting
C. Jaundice
D. Rash
Answer: B

11. Rice-water stools are characteristic of:

A. Salmonella
B. Vibrio cholerae
C. Staph
D. E. coli
Answer: B

12. Gram-positive cocci in clusters indicate:

A. Salmonella
B. E. coli
C. Staphylococcus aureus
D. Vibrio
Answer: C

13. MacConkey agar is selective for:

A. Gram-positive bacteria
B. Gram-negative bacteria
C. Viruses
D. Parasites
Answer: B

14. XLD agar is used for:

A. Staphylococcus
B. Salmonella
C. Vibrio
D. Clostridium
Answer: B

15. Food infection differs from intoxication because:

A. Toxin is preformed
B. Organism multiplies in intestine
C. No bacteria involved
D. No symptoms
Answer: B

16. The most important treatment in food poisoning is:

A. Steroids
B. Antibiotics always
C. ORS
D. Surgery
Answer: C

17. Hemolytic uremic syndrome is complication of:

A. Vibrio
B. Staph
C. Escherichia coli
D. Norovirus
Answer: C

18. The best specimen for diagnosis is:

A. Urine
B. Stool
C. CSF
D. Saliva
Answer: B

19. Widal test is used for:

A. Cholera
B. Salmonella
C. Staph
D. E. coli
Answer: B

20. Coagulase test identifies:

A. Salmonella
B. Vibrio
C. Staphylococcus aureus
D. E. coli
Answer: C

21. Anaerobic spore-forming bacillus:

A. E. coli
B. Staph
C. Clostridium perfringens
D. Vibrio
Answer: C

22. Most common source of Salmonella:

A. Eggs
B. Fruits
C. Water only
D. Air
Answer: A

23. Viral food poisoning spreads rapidly due to:

A. Spores
B. Toxins
C. High infectivity
D. Antibiotics
Answer: C

24. ELISA is useful for detecting:

A. Bacteria culture
B. Viral antigens
C. Parasite eggs
D. RBC count
Answer: B

25. Severe dehydration leads to:

A. Shock
B. Hypertension
C. Diabetes
D. Cancer
Answer: A

26. Heat-stable enterotoxin is produced by:

A. Salmonella
B. Clostridium perfringens
C. Vibrio cholerae
D. Staphylococcus aureus
Answer: D

27. Multiplex PCR is useful because it:

A. Detects only one pathogen
B. Detects multiple pathogens simultaneously
C. Replaces culture completely
D. Detects parasites only
Answer: B

28. Zinc supplementation is especially recommended in:

A. Adults
B. Elderly
C. Children with diarrhea
D. Pregnant women
Answer: C

29. Outbreaks in hostels and cruise ships are commonly caused by:

A. Salmonella
B. Staphylococcus
C. Norovirus
D. Clostridium
Answer: C

30. Citrate utilization test is used to differentiate:

A. Gram-positive cocci
B. Enterobacteriaceae members
C. Viruses
D. Parasites
Answer: B

31. Indole-positive organism commonly causing food poisoning:

A. Salmonella
B. Vibrio
C. Shigella
D. Escherichia coli
Answer: D

32. The most important preventive measure is:

A. Antibiotics
B. Vaccination only
C. Hand washing
D. Antacids
Answer: C

33. Food poisoning cases are more common during:

A. Winter
B. Rainy season only
C. Summer
D. Autumn
Answer: C

34. Septicemia is a serious complication of:

A. Norovirus
B. Staphylococcus
C. Salmonella enterica
D. Giardia
Answer: C

35. Gram-negative comma-shaped bacillus:

A. E. coli
B. Salmonella
C. Vibrio cholerae
D. Staphylococcus
Answer: C

36. Ova and cysts are detected in:

A. Bacterial infection
B. Viral infection
C. Chemical poisoning
D. Parasitic infection
Answer: D

37. Most rapid onset of symptoms occurs in:

A. Salmonella infection
B. E. coli infection
C. Staphylococcus aureus intoxication
D. Hepatitis A
Answer: C

38. High-risk groups for severe food poisoning include:

A. Healthy adults
B. Teenagers
C. Children and elderly
D. Athletes
Answer: C

39. Improper refrigeration promotes growth of:

A. Pathogenic bacteria
B. Viruses
C. Fungi only
D. Parasites only
Answer: A

40. Catalase-positive Gram-positive cocci:

A. Streptococcus
B. Staphylococcus aureus
C. Salmonella
D. Vibrio
Answer: B

41. Lactose fermenting colonies on MacConkey agar appear:

A. Colorless
B. Black
C. Pink
D. Green
Answer: C

42. Non-lactose fermenter on MacConkey agar:

A. E. coli
B. Salmonella enterica
C. Klebsiella
D. Enterobacter
Answer: B

43. Major fluid loss in cholera is due to:

A. RBC destruction
B. Electrolyte secretion
C. Toxin-induced water and electrolyte loss
D. Liver damage
Answer: C

44. Stool culture is important in:

A. Outbreak investigation
B. Viral hepatitis only
C. Diabetes
D. Hypertension
Answer: A

45. Food handler hygiene prevents:

A. Genetic diseases
B. Fecal-oral transmission
C. Viral mutation
D. Chemical poisoning
Answer: B

46. PCR in food poisoning helps to:

A. Detect toxin genes
B. Replace microscopy
C. Detect RBC
D. Measure glucose
Answer: A

47. Blood culture is indicated when:

A. Only vomiting
B. Mild diarrhea
C. Fever and systemic signs
D. No symptoms
Answer: C

48. Antibiotics are usually NOT required in:

A. Salmonella septicemia
B. E. coli HUS
C. Staphylococcus aureus intoxication
D. Shigella dysentery
Answer: C

49. Main mode of transmission of food poisoning:

A. Airborne
B. Vector-borne
C. Fecal-oral route
D. Blood transfusion
Answer: C

50. The most important role of MLT in food poisoning is:

A. Prescribing antibiotics
B. Performing surgery
C. Accurate laboratory identification
D. Counseling patients
Answer: C

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