Food poisoning

Definition

Food poisoning refers to illness caused by ingestion of food or drink contaminated with pathogenic microorganisms, toxins, or chemicals. It encompasses a range of acute gastrointestinal syndromes, with symptoms developing from hours to days after ingestion, depending on the causative agent.

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Etiology

Food poisoning can be classified based on the causative agent:

1. Bacterial causes

• Salmonella spp. – undercooked poultry, eggs, unpasteurised milk

• Escherichia coli (E. coli) – especially E. coli O157:H7 from contaminated beef, produce

• Clostridium perfringens – cooked meat left at unsafe temperatures

• Listeria monocytogenes – soft cheeses, deli meats, unpasteurised dairy

• Campylobacter jejuni – undercooked poultry, contaminated water

• Staphylococcus aureus – toxins in dairy products, salads, cream-filled pastries

• Vibrio parahaemolyticus – undercooked seafood

• Bacillus cereus – reheated rice and starchy foods

2. Viral causes

• Norovirus – contaminated shellfish, water, person-to-person spread

• Rotavirus – contaminated food or water, common in children

3. Parasitic causes

• Giardia lamblia – contaminated water or food

• Toxoplasma gondii – undercooked meat, contaminated produce

4. Toxin-related food poisoning

• Ciguatera toxin – reef fish

• Scombrotoxin – spoiled fish (tuna, mackerel)

• Botulinum toxin (Clostridium botulinum) – improperly canned foods

• Mycotoxins – mould-contaminated grains and nuts

5. Chemical contamination

• Pesticides, heavy metals, cleaning agents accidentally ingested in food

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Pathophysiology

• Infective type: microorganisms invade and multiply in the gut mucosa, causing inflammation and sometimes systemic spread

• Toxin-mediated type: pre-formed toxins in food cause symptoms without bacterial colonisation (e.g., S. aureus, B. cereus)

• Chemical type: toxic agents cause direct mucosal irritation or systemic toxicity

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Risk Factors

• Poor food hygiene and handling

• Improper storage (temperature abuse)

• Consumption of raw or undercooked meat, seafood, or eggs

• Unpasteurised dairy products

• Immunocompromised states (HIV, chemotherapy, pregnancy)

• Extremes of age (infants, elderly)

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Clinical Presentation

Symptoms (onset varies by agent – can be 1 hour to several days):

• Nausea

• Vomiting

• Diarrhoea (may be watery or bloody)

• Abdominal cramps

• Fever and chills

• Headache, myalgia (some viral causes)

• Neurological symptoms in certain toxin-mediated cases (botulism, ciguatera)

Severe symptoms requiring urgent attention:

• Persistent vomiting preventing fluid intake

• High fever (>38.5°C)

• Bloody diarrhoea

• Signs of dehydration (dry mucous membranes, oliguria, hypotension)

• Neurological deficits

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Diagnosis

Clinical evaluation

• Detailed food history (what, where, when eaten)

• Symptom onset timing and progression

• Other affected individuals (outbreak suspicion)

Laboratory tests (if severe, prolonged, or outbreak suspected):

• Stool culture for bacterial pathogens (Salmonella, Shigella, Campylobacter, E. coli O157:H7)

• Stool PCR panels for viruses and bacteria

• Stool microscopy for ova and parasites

• Blood tests (electrolytes, renal function) for severe dehydration

• Toxin assays in suspected botulism or staphylococcal food poisoning

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Management

Treatment is primarily supportive; specific antimicrobial therapy is reserved for select cases.

1. Rehydration and Electrolyte Replacement

• Oral rehydration solution (ORS): glucose-electrolyte formula; small frequent sips

• Severe dehydration: intravenous fluids (normal saline or Ringer’s lactate)

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2. Symptomatic Treatment

• Antiemetics (if vomiting severe):

  • Ondansetron 4–8 mg orally/IV every 8 hours as needed

  • Metoclopramide 10 mg orally/IV every 8 hours as needed

• Antidiarrhoeals (avoid in bloody diarrhoea or suspected invasive bacterial infection):

  • Loperamide 4 mg orally initially, then 2 mg after each loose stool (max 16 mg/day) in non-invasive diarrhoea only

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3. Antimicrobial Therapy (selected cases)

Antibiotics are indicated for:

• Severe bacterial gastroenteritis with high fever and dysentery (Shigella, Campylobacter, severe Salmonella)

• Immunocompromised patients

• Listeriosis (pregnant women, neonates, elderly)

Examples:

• Azithromycin 500 mg orally once daily for 3 days (Campylobacter, traveller’s diarrhoea)

• Ciprofloxacin 500 mg orally twice daily for 3 days (non-resistant Salmonella, Shigella) – avoid in children unless benefits outweigh risks

• Amoxicillin 500 mg orally three times daily for 7–10 days (Listeria)

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4. Special Cases

• Botulism: urgent hospitalisation, administration of botulinum antitoxin, supportive ventilation if respiratory failure

• Parasitic infections:

  • Giardiasis – Metronidazole 400 mg orally three times daily for 5–7 days

  • Toxoplasmosis – pyrimethamine + sulfadiazine + folinic acid in immunocompromised or pregnant patients (specialist-guided)

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Prevention

• Proper cooking of meat, seafood, and eggs

• Avoid raw milk and unpasteurised dairy products

• Hand hygiene before food preparation and eating

• Safe food storage (refrigeration below 5°C, hot holding above 60°C)

• Separation of raw and cooked foods to prevent cross-contamination

• Clean utensils and surfaces after handling raw products

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Prognosis

• Most cases are self-limiting within 24–72 hours

• Severe disease possible in extremes of age, immunocompromised, or with highly virulent/toxic pathogens

• Mortality is rare except in severe outbreaks or toxin-mediated cases (botulism, severe listeriosis)