SN5 SHORT NOTE 5M

Write a short note on food poisoning.

General Medicine · Final Professional

Definition

Food poisoning is illness resulting from the ingestion of food or water contaminated with pathogenic organisms, their toxins, or chemical substances. It is a leading cause of morbidity in India, particularly in the summer and monsoon, and outbreaks are frequently linked to social gatherings, street food and inadequate refrigeration.

Classification BY Mechanism and Incubation Period

The incubation period is the single most useful clue to the organism — a question examiners like:

Incubation	Organism	Source	Features
1–6 hours	Staphylococcus aureus (preformed enterotoxin)	Custard, cream, dairy, cooked meat handled by a carrier with a skin lesion	Violent vomiting, abdominal cramps, little or no fever; short-lived
1–6 hours	Bacillus cereus — emetic toxin	Reheated rice — the classic association	Vomiting predominates
8–16 hours	Bacillus cereus — diarrhoeal toxin; Clostridium perfringens	Meat, gravy, stews kept warm	Watery diarrhoea and cramps, minimal vomiting
12–48 hours	Salmonella (non-typhoidal)	Poultry, eggs, meat, unpasteurised milk	Fever, diarrhoea (may be bloody), cramps
12–72 hours	Vibrio parahaemolyticus	Seafood, shellfish	Watery diarrhoea, cramps
1–3 days	Vibrio cholerae	Contaminated water, seafood	Profuse painless "rice-water" stools, rapid dehydration, no fever
2–5 days	Campylobacter jejuni	Poultry, unpasteurised milk	Bloody diarrhoea, fever, abdominal pain; Guillain–Barré syndrome as a sequel
1–8 days	Escherichia coli O157:H7 (EHEC/STEC)	Undercooked beef, contaminated produce	Bloody diarrhoea without fever; haemolytic uraemic syndrome
12–72 hours	Clostridium botulinum	Home-canned and bottled foods, honey (infants)	Descending flaccid paralysis, diplopia, ptosis, bulbar palsy — with a CLEAR sensorium and NO fever
Days–weeks	Listeria monocytogenes	Soft cheese, deli meats, unpasteurised milk	Febrile gastroenteritis; meningitis in pregnancy, neonates, elderly and immunosuppressed
Minutes–hours	Non-infective — mushroom toxins, scombroid (histamine) poisoning from spoiled fish, ciguatera, pesticide contamination, heavy metals	—	Scombroid: flushing, headache, palpitations, urticaria — resembles allergy, responds to antihistamines

Clinical Assessment

History: the incubation period, nature of symptoms (vomiting-predominant suggests preformed toxin; diarrhoea-predominant suggests enterotoxin or invasion), presence of blood in the stool, fever, the specific food eaten and its handling, whether others who shared the meal are affected (a common-source outbreak), travel, and antibiotic use in the preceding weeks (*Clostridioides difficile*).

Examination: the essential task is to assess dehydration and haemodynamic status — mucous membranes, skin turgor, capillary refill, pulse, blood pressure, postural drop, urine output and level of consciousness. Also assess for abdominal tenderness, and for neurological signs suggesting botulism.

Red flags requiring admission and investigation: severe dehydration or shock, bloody diarrhoea, high fever, severe abdominal pain or peritonism, neurological features, immunosuppression, extremes of age, pregnancy, and symptoms persisting beyond a week.

Investigations

Most cases are mild and self-limiting and need no investigation. Where indicated:

Stool microscopy, culture and sensitivity; stool for ova and parasites if the illness is prolonged; *C. difficile* toxin where there is preceding antibiotic use.
Blood cultures where there is fever with systemic illness.
CBC, urea, electrolytes and creatinine — to assess dehydration and detect acute kidney injury; CBC and blood film with renal function in suspected HUS (anaemia with schistocytes, thrombocytopenia, renal failure).
Sigmoidoscopy in persistent bloody diarrhoea to exclude inflammatory bowel disease.
Public health notification and sampling of the implicated food in outbreaks.

Management

1. Rehydration is the treatment — everything else is secondary.

Oral rehydration solution for mild to moderate dehydration; frequent small volumes; continue feeding, including breastfeeding in infants.
Intravenous fluids (Ringer's lactate or normal saline) for severe dehydration, shock, persistent vomiting or inability to drink.
Correct electrolyte disturbance — hypokalaemia is common with profuse diarrhoea.

2. Symptomatic

Antiemetics (ondansetron) for troublesome vomiting.
Antimotility agents (loperamide) may be used in mild watery diarrhoea in adults, but must be AVOIDED in bloody diarrhoea, fever, suspected dysentery, EHEC and *C. difficile* — they prolong exposure to toxin and increase the risk of toxic megacolon and HUS.
Zinc supplementation in children with diarrhoea.

3. Antibiotics — used selectively, not routinely

Most bacterial food poisoning is self-limiting and antibiotics are unnecessary and may prolong carriage. They are indicated for: cholera (shortens illness and reduces transmission), shigellosis and invasive salmonellosis with systemic illness, campylobacter with severe or prolonged disease, enteric fever, traveller's diarrhoea in some circumstances, listeriosis, and severe disease in the immunocompromised, the elderly and infants.

Antibiotics are specifically CONTRAINDICATED in *E. coli* O157:H7, where they increase the risk of haemolytic uraemic syndrome by promoting toxin release.

4. Specific treatments — botulinum antitoxin and ventilatory support for botulism; antihistamines for scombroid; and specific antidotes for chemical poisoning.

5. Public health — notify outbreaks, investigate the source, exclude affected food handlers, and inspect premises.

Prevention

Safe water, hand hygiene, thorough cooking, prompt refrigeration (avoiding the 5–60 °C "danger zone"), avoiding cross-contamination between raw and cooked food, avoiding reheating rice, pasteurisation of milk, and food handler education and screening. In the Indian setting, particular attention is needed to street food, ice, cut fruit and water quality at social gatherings, where large outbreaks originate.

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