Doctors Revision

Toxicology / Poisoning

Food Poisoning

Illness caused by consumption of food or water contaminated with pathogenic microorganisms (bacteria, viruses, parasites) or their toxins. Often presents as acute gastroenteritis, potentially affecting multiple people who consumed the same source.

Also known as: Foodborne Illness, Gastroenteritis (infectious etiology via food), Stomach Flu (colloquial)

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Referral and warning signs

When to refer

Refer to Hospital (HC2/HC3/H) if: Signs of severe dehydration (lethargy, unable to drink, prolonged capillary refill, hypotension). Persistent vomiting preventing oral rehydration. High fever (>38.5°C). Bloody diarrhoea (dysentery). Severe abdominal pain. Symptoms persisting >3-7 days without improvement. Signs of complications (e.g., decreased urine output, altered mental status). Patient is very young (<6 months), elderly, pregnant, or immunocompromised.

Red flags

  • Signs of severe dehydration or shock
  • Bloody diarrhoea
  • High fever (>38.5 - 39°C)
  • Severe, persistent abdominal pain
  • Altered mental status or lethargy
  • Decreased or no urine output
  • Persistent vomiting preventing oral intake

Signs and symptoms

  • Common symptoms (vary depending on pathogen and incubation period):
  • - Nausea
  • - Vomiting
  • - Abdominal pain (often cramping or colicky)
  • - Diarrhoea (may be watery or bloody/dysenteric depending on cause)
  • - Fever (more common with invasive bacterial infections like Salmonella, Campylobacter, Shigella)
  • - Headache, malaise, muscle aches
  • Specific features depend on cause:
  • - Rapid onset (1-6 hours) vomiting predominant: Suggests preformed toxins (Staphylococcus aureus, Bacillus cereus emetic type).
  • - Watery diarrhoea, cramps (8-16 hours): Suggests Clostridium perfringens, Bacillus cereus diarrheal type.
  • - Watery or bloody diarrhoea, fever, cramps (1-3 days): Suggests Salmonella, Campylobacter, Shigella, E. coli (EHEC/STEC), Vibrio.
  • - Prolonged watery diarrhoea: Suggests parasites (Giardia, Cryptosporidium) or viruses (Norovirus, Rotavirus).
  • - Botulism (rare, neurotoxin): Descending paralysis (blurred/double vision, difficulty swallowing/speaking, muscle weakness), typically without fever or GI symptoms initially.

Risk factors

  • Consumption of improperly cooked or stored food (especially meat, poultry, eggs, seafood, dairy products, rice).
  • Consumption of contaminated raw fruits or vegetables.
  • Consumption of unpasteurized milk or juice.
  • Consumption of contaminated water.
  • Poor personal hygiene practices by food handlers.
  • Cross-contamination in kitchens.
  • Eating at large gatherings, restaurants, or institutions where food safety may lapse.

Diagnosis

Clinical assessment

Based on history of acute onset GI symptoms (nausea, vomiting, diarrhoea, abdominal pain) following consumption of potentially contaminated food or water. Often involves multiple people exposed to the same source (outbreak). Assess hydration status carefully.

Investigations

  • Usually diagnosed clinically, investigations often not needed for mild, self-limiting cases.
  • Stool Examination:
  • - Microscopy: Look for fecal leukocytes (suggests inflammatory/invasive bacterial cause like Shigella, Salmonella, Campylobacter), ova, cysts, parasites.
  • - Stool Culture & Sensitivity (C&S): Indicated if severe illness, bloody diarrhoea (dysentery), high fever, prolonged symptoms (>3-7 days), immunocompromised host, or during outbreak investigation.
  • - Specific tests (e.g., Shiga toxin assay for EHEC/STEC, Clostridium difficile toxin assay if recent antibiotic use/hospitalization) based on clinical suspicion.
  • Blood tests (Consider if severe dehydration, sepsis suspected): CBC, Electrolytes, Renal function.
  • Blood cultures if systemic infection/sepsis suspected (high fever, rigors, severe illness).

Diagnostic criteria

Acute onset of compatible GI symptoms following potential exposure to contaminated food/water, often supported by epidemiological link (others ill from same source).

Management

Non-pharmacological management

  • Rehydration (Mainstay of treatment):
  • - Oral Rehydration Therapy (ORT): Use Oral Rehydration Salts (ORS) solution for mild to moderate dehydration. Encourage frequent small sips. Also allow other clear fluids (water, soup) and usual diet as tolerated.
  • - Intravenous (IV) Fluids: Use Normal Saline or Ringer's Lactate for severe dehydration, persistent vomiting preventing ORT, or signs of shock. Follow standard dehydration management protocols (see EM003 - Dehydration Management).
  • Dietary Advice: Continue feeding as tolerated. Avoid sugary drinks, fatty or spicy foods initially. Breastfeeding should continue.
  • Symptomatic Relief: Rest.

Pharmacological treatment

  • Antidiarrheals (e.g., Loperamide): Generally AVOID in suspected inflammatory/bloody diarrhoea or high fever, as they may prolong illness or worsen outcome (e.g., toxic megacolon in C. difficile, HUS risk in EHEC). May consider for mild-moderate watery diarrhoea without fever/blood for symptomatic relief.
  • Antiemetics (e.g., Ondansetron, Promethazine): May be used cautiously for severe vomiting interfering with ORT, but rehydration is priority.
  • Analgesics/Antipyretics: Paracetamol for fever or abdominal pain (Adult: 1g q4-6h; Child: 10-15mg/kg/dose).
  • Antibiotics: NOT routinely indicated for most cases of food poisoning (often viral or self-limiting bacterial). Reserve for specific situations:
  • - Suspected or confirmed invasive bacterial infection: Severe illness, high fever, bloody diarrhoea (dysentery), immunocompromised patient.
  • - Specific pathogens: Shigellosis, Cholera, Traveler's diarrhea (severe), Campylobacter (if severe/prolonged), Salmonella (only if severe, bacteremic, or high-risk host).
  • - Choice based on likely pathogen and local resistance patterns (UCG recommends Ciprofloxacin or Erythromycin). Example: Ciprofloxacin 500mg PO q12h for 3-7 days (Adult); Erythromycin 500mg PO q6h for 3-7 days (Adult). Child doses: Cipro 10-15mg/kg q12h; Erythro 10-12.5mg/kg q6h.
  • - Avoid antibiotics for suspected EHEC/STEC (may increase risk of Hemolytic Uremic Syndrome - HUS).
  • Specific treatment for Botulism: Requires antitoxin and intensive supportive care (Hospital/RR).

Monitoring

Monitor hydration status closely (clinical signs, urine output, vital signs). Monitor frequency and nature of stool/vomit. Monitor temperature. Reassess if symptoms worsen or persist beyond several days.

Complications

  • Dehydration (most common)
  • Electrolyte imbalances
  • Hypovolemic shock (severe dehydration)
  • Reactive arthritis (esp. after Salmonella, Shigella, Campylobacter)
  • Guillain-Barré syndrome (esp. after Campylobacter)
  • Hemolytic Uremic Syndrome (HUS) (esp. after EHEC/STEC O157:H7)
  • Toxic megacolon (rare, e.g., C. difficile)
  • Bacteremia/Sepsis (with invasive organisms)
  • Malnutrition (if prolonged diarrhoea)

Prevention

  • Food Safety Practices ('Five Keys to Safer Food' - WHO):
  • 1. Keep Clean: Wash hands frequently, clean surfaces and utensils.
  • 2. Separate Raw and Cooked: Avoid cross-contamination.
  • 3. Cook Thoroughly: Especially meat, poultry, eggs, seafood.
  • 4. Keep Food at Safe Temperatures: Refrigerate promptly, don't leave cooked food at room temperature for >2 hours.
  • 5. Use Safe Water and Raw Materials: Wash fruits/vegetables, use potable water.
  • Ensure adequate personal hygiene (handwashing after toilet use, before handling food).
  • Proper sanitation and sewage disposal.
  • Avoid unpasteurized dairy products.
  • Careful food selection when travelling.
  • Breastfeeding protects infants.

Patient education

  • Explain the likely cause is contaminated food/water.
  • Emphasize importance of fluid replacement (ORS is best).
  • Advise on diet as tolerated.
  • Explain warning signs requiring immediate return to facility (Red Flags).
  • Educate on food safety practices and hygiene to prevent recurrence and spread.

Uganda-specific notes

Foodborne illnesses are common due to challenges with sanitation, safe water access, and food storage/handling. Cholera outbreaks occur. Always consider common bacterial pathogens like Salmonella, Shigella, Campylobacter. Focus is on rehydration (ORT). Antibiotic use should be selective based on severity and likely pathogen (refer to UCG for empiric choices). Public health measures are crucial for prevention.

References

  • Uganda Clinical Guidelines (UCG) 2023

    Chapter 1, Section 1.3.13

  • Uganda Clinical Guidelines (UCG) 2023

    Chapter 2 (Management of Diarrhoea/Gastroenteritis - likely contains more detailed info)

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