Food Poisoning

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Food poisoning is an illness caused by consuming contaminated food or drinks, leading to symptoms such as nausea, vomiting, diarrhoea, and abdominal pain. It is commonly caused by bacterial, viral, or parasitic infections.

Aetiology

1. Bacterial Causes (Most Common):

• Salmonella: found in raw poultry, eggs, and dairy.
• Escherichia coli (E. coli): common in undercooked beef, unpasteurised milk.
• Campylobacter: present in contaminated poultry, raw milk.
• Shigella: causes dysentery, associated with contaminated water.
• Clostridium perfringens: produces toxins in improperly stored cooked food.
• Staphylococcus aureus: produces heat-stable toxins in contaminated food.
• Bacillus cereus: found in reheated rice and starchy foods.

2. Viral Causes:

• Norovirus: most common cause of viral gastroenteritis, spreads via contaminated food and surfaces.
• Rotavirus: affects infants and young children, now reduced due to vaccination.

3. Parasitic Causes:

• Giardia lamblia: found in contaminated water sources.
• Cryptosporidium: waterborne outbreaks.

Pathophysiology

• Pathogens enter the gastrointestinal tract through contaminated food or water.
• They produce toxins that damage the intestinal lining, leading to diarrhoea and vomiting.
• Some bacteria (e.g., Shigella, Salmonella) invade the gut lining, causing inflammation.
• Viral infections cause fluid secretion into the intestines, leading to watery diarrhoea.

Risk factors

• Consumption of undercooked or raw meat, seafood, eggs.
• Unpasteurised dairy products.
• Contaminated water sources.
• Poor hygiene and improper food handling.
• Travelling to high risk areas ("traveller’s diarrhoea").
• Weakened immune system (e.g., elderly, infants, immunocompromised individuals).

Signs and symptoms

• Diarrhoea: watery (viral), bloody (bacterial dysentery).
• Nausea and vomiting: Sudden onset, often in viral infections.
• Abdominal cramps and pain.
• Fever: common in bacterial infections.
• Signs of dehydration: dry mouth, dizziness, reduced urine output.

Investigations

• Clinical diagnosis: based on history of food consumption and symptoms.
• Stool culture: indicated if:
  • Severe or prolonged diarrhoea (>7 days).
  • Bloody stools (suggests bacterial cause).
  • Recent travel history (rule out parasites).
  • Immunocompromised patient.
• Blood tests:
  • Urea and electrolytes (assess dehydration, hypokalaemia).
  • Full blood count (raised white cells suggest bacterial infection).

Management

1. Supportive Care:

• Oral rehydration therapy (ORT): first line for mild to moderate dehydration (e.g., Dioralyte®).
• IV fluids: if severe dehydration or unable to tolerate oral fluids.
• Antipyretics: paracetamol for fever.
• Antiemetics: Stemitil (Prochlorperazine) or other antiemetics may be considered for severe vomiting.

2. Specific Treatment:

• Viral food poisoning: supportive care only; antibiotics not required.
• Bacterial food poisoning: most cases are self limiting, but antibiotics may be needed for:
  • Severe or persistent symptoms.
  • Immunocompromised patients.
  • Specific infections (e.g., ciprofloxacin for severe traveller’s diarrhoea).
• Parasitic infections: metronidazole for Giardia.

3. Prevention:

• Proper food hygiene (cook meat thoroughly, avoid raw seafood).
• Hand washing with soap and water before eating and after handling food.
• Safe food storage (keep raw and cooked food separate).
• Use clean drinking water (boil or purify when travelling).