Food Poisoning

EM Notes – Foodborne Illness

Causative Agents

**Source and Clinical Features


**Diagnosis and Treatment


Improperly stored foods with high salt or sugar content favour growth of staphylococci

Intense vomiting and watery diarrhoea start 1–4 hours after ingestion and last as long as 24–48 hours.

Enterotoxin acts on receptors in gut that transmit impulses to medullary centers.

Symptomatic treatment

B cereus

Contaminated fried rice (emetic). Meatballs (diarrheal)

Emetic: Duration is 9 hours, vomiting and cramps

Diarrheal: Lasts for 24 h

Mainly vomiting after 1–6 hours and mainly diarrhoea after 8–16 hours after ingestion; lasts as long as 1 day

Emetic enterotoxin (short incubation and duration) – Poorly understood

Diarrheal enterotoxin (long incubation and duration) – Increasing intestinal secretion by activation of adenylate cyclase in intestinal epithelium

Symptomatic treatment

C perfringens

Inadequately cooked meat, poultry, or legumes

Acute onset of abdominal cramps with diarrhoea starts 8–24 hours after ingestion.

Vomiting is rare. It lasts less than 1 day.

Enteritis necroticans associated with C perfringens type C in improperly cooked pork (40% mortality)

Enterotoxin produced in the gut, and food causes hypersecretion in the small intestine.

Culture of clostridia in food and stool

Symptomatic treatment

C botulinum

Canned foods (e.g., smoked fish, mushrooms, vegetables, honey)

Descending weakness and paralysis start 1–4 days after ingestion, followed by constipation.

Mortality is very high.

Toxin absorbed from the gut blocks the release of acetylcholine in the neuromuscular junction.

Toxin present in food, serum, and stool.

Respiratory support

Intravenous trivalent antitoxin from CDC

Listeria monocytogenes

Raw and pasteurized milk, soft cheeses, raw vegetables, shrimp

Systemic disease associated with bacteraemia

Intestinal symptoms precede systemic disease

Can seed meninges, heart valves, and other organs

Highest mortality among bacterial food poisonings

Highly motile, heat-resistant, gram-positive organism

CSF or blood culture

Must treat with antibiotics if bacteraemic

Enterotoxic E coli (e.g., traveller’s diarrhoea)

Contaminated water and food (e.g., salad, cheese, meat)

Acute-onset watery diarrhoea starts 24–48 hours after ingestion.

Vomiting and abdominal cramps may be present. Lasts 1–2d

Enterotoxin causes hypersecretion in small and large intestine via guanylate cyclase activation.

Supportive treatment

No antibiotics

Enterohaemorrhagic E coli (e.g., E coli O157:H7)

Improperly cooked hamburger meat and previously spinach

Commonest pathogen in bloody diarrhoea starts 3–4d after ingestion.

Usually progresses from watery to bloody diarrhoea. It lasts for 3–8 days

May be complicated by HUS or TTP

Cytotoxin results in endothelial damage and leads to platelet aggregation and microvascular fibrin thrombi

Diagnosis with stool culture

Supportive treatment

No antibiotics

Enteroinvasive_E coli_

Contaminated imported cheese

Usually watery diarrhoea (some may present with dysentery)

Enterotoxin produces secretion

Shiga-like toxin facilitates invasion.

Supportive treatment

No antibiotics

Enteroaggregative E coli

Implicated in traveller’s diarrhoea in developing countries

Can cause bloody diarrhoea

Bacteria clump on the cell surfaces

Ciprofloxacin may shorten duration and eradicate the organism

V cholera

Contaminated water and food

Large amount of nonbloody diarrhoea starts 8–24 hours after ingestion. It lasts for 3–7 days.

Enterotoxin causes hypersecretion in small intestine.

Infective dose usually is 107 –109 organisms.

Positive stool culture

Prompt replacement of fluids and electrolytes (oral rehydration solution)

Tetracycline (or fluoroquinolones) shortens the duration of symptoms and excretion of Vibrio.

Causative Agents

Source and Clinical Features


Diagnosis and Treatment

V parahaemolyticus

Raw and improperly cooked seafood (i.e., molluscs and crustaceans)

Explosive watery diarrhoea starts 8–24 hours after ingestion. It lasts for 3–5 days.

Enterotoxin causes hypersecretion in small intestine.

Haemolytic toxin is lethal.

Infective dose usually is 107 –109 organisms.

Positive stool culture

Prompt replacement of fluids and electrolytes

Sensitive to tetracycline, but unclear role for antibiotics

V vulnificus

Wound infection in salt water or consumption of raw oysters

Can be lethal in patients with liver disease (50% mortality)

Polysaccharide capsule

Growth correlates with availability of iron (esp. transferrin saturation >70%)

Culture of characteristic bullous lesions or blood

Immediate antibiotics if suspected (e.g., doxycycline and ceftriaxone)

C jejuni

Domestic animals, cattle, chickens

Faecal-oral transmission in humans

Foul-smelling watery diarrhoea followed by bloody diarrhoea

Abdominal pain and fever also may be present. It starts 1–3 days after exposure and recovery is in 5–8 days.

Uncertain about endotoxin production and invasion

Culture in special media at 42°C

Erythromycin for invasive disease (fever)


Potato, egg salad, lettuce, vegetables, milk, ice cream, and water

Abrupt onset of bloody diarrhoea, cramps, tenesmus, and fever starts 12–30 hours after ingestion.

Usually self-limited in 3–7 days

Organisms invade epithelial cells and produce toxins.

Infective dose is 102 –103 organisms.

Enterotoxin-mediated diarrhoea followed by invasion (dysentery/colitis)

Polymorphonuclear leukocytes (PMNs), blood, and mucus in stool

Positive stool culture

Oral rehydration is mainstay.

Trimethoprim-sulfamethoxazole (TMP-SMX) or ampicillin for severe cases

No opiates


Beef, poultry, eggs, and diary products Abrupt onset of moderate-to-large amount of diarrhoea with low-grade fever; in some cases, bloody diarrhoea

Abdominal pain and vomiting also present, beginning 6–48 hours after exposure and lasts 7–12 days

Invasion but no toxin production

Positive stool culture

Antibiotic for systemic infection


Pets; transmission in humans by faecal-oral route or contaminated milk or ice cream

Acute abdominal pain, diarrhoea, and fever (enterocolitis)

Incubation period not known Polyarthritis and erythema nodosum in children

May mimic appendicitis

Gastroenteritis and mesenteric adenitis

Direct invasion and enterotoxin

PMNs and blood in stool

Positive stool culture

No evidence that antibiotics alter the course but may be used in severe infections


Untreated well or spring water

Diarrhoea may be bloody.

May be chronic up to 42 days in the United States

Enterotoxin, haemolysin, and cytotoxin

Positive stool culture

Fluoroquinolones or TMP/SMX for chronic diarrhoea

Parasitic Food Poisoning

Source and Clinical Features


Diagnosis and Treatment

E histolytica

Contaminated food and water

90% asymptomatic

10% dysentery

Minority may develop liver abscesses

Invasion of the mucosa by the parasites

Criterion standard is colonoscopy with biopsy

Ova and parasites may be seen in the stool but has low sensitivity

Luminal amebicides (e.g., paromomycin) Tissue amebicides (e.g., metronidazole)

G lamblia

Contaminated ground water

Faecal-oral transmission in humans

Mild bloody diarrhoea with nausea and abdominal cramps starts 2–3 days after ingestion; lasts for 1 week

May become chronic


Highest concentration in the distal duodenum and proximal jejunum

Initial diagnostic test is stool ELISA

Duodenal aspiration or small bowel biopsy

Cyst in the stool


Seafood/Shellfish Poisoning

**Source and Clinical Features


**Diagnosis and Treatment

Paralytic shellfish poisoning

Temperate costal areas

Source – Bivalve molluscs

Onset usually is 30–60 minutes.

Initial symptoms include perioral and intraoral paraesthesia.

Other symptoms include paraesthesia of the extremities, headache, ataxia, vertigo, cranial nerve palsies, and paralysis of respiratory muscles, resulting in respiratory arrest.

Fish acquires toxin-producing dinoflagellates

General observation for 4–6 hours

Maintain patent airway.

Administer oxygen, and assist ventilation if necessary.

For recent ingestion, charcoal 50–60 g may be helpful.

Neurotoxic shellfish poisoning

Coastal Florida

Source – Molluscs

Illness is milder than in paralytic shellfish poisoning.

Fish acquires toxin-producing dinoflagellates



Hawaii, Florida, and Caribbean

Source – Carnivorous reef fish

Vomiting, diarrhoea, and cramps start 1–6 hours after ingestion and last from days to months.

Diarrhoea may be accompanied by a variety of neurologic symptoms including paraesthesia, reversal of hot and cold sensation, vertigo, headache, and autonomic disturbances such as hypotension and bradycardia.

Chronic symptoms (e.g., fatigue, headache) may be aggravated by caffeine or alcohol

Fish acquires toxin-producing dinoflagellates

Toxin increases intestinal secretion by changing intracellular calcium concentration


Anecdotal reports of successful treatment of neurologic symptoms with mannitol 1 g/kg IV

Tetrodotoxin poisoning


Source – Puffer fish

Onset of symptoms usually is 30–40 minutes but may be as short as 10 minutes. It includes lethargy, paraesthesia, emesis, ataxia, weakness, and dysphagia. Ascending paralysis occurs in severe cases. Mortality is high.

Neurotoxin is concentrated in the skin and viscera of puffer fish.



Source – Tuna, mahi-mahi, kingfish

Allergic symptoms such as skin flush, urticaria, bronchospasm, and hypotension usually start within 15–90 minutes.

Improper preservation of large fish results in bacterial degradation of histidine to histamine.

Antihistamines (diphenhydramine 25–50 mg IV)

H2 blockers (cimetidine 300 mg IV)

Severe reactions may require IM adrenaline (0.3–0.5 mL of 1:1000 solution).

Heavy Metal Poisoning





Ingestion of inorganic mercuric salts

Causes metallic taste, salivation, thirst, discoloration and oedema of oral mucous membranes, abdominal pain, vomiting, bloody diarrhoea, and acute renal failure

Consult a toxicologist.

Remove ingested salts by emesis and lavage, and administer activated charcoal and a cathartic.

Dimercaprol is useful in acute ingestion.


Toxicity results from chronic repeated exposure.

It is rare after single ingestion.

Common symptoms include colicky abdominal pain, constipation, headache, and irritability.

Diagnosis is based on lead level (>10 mcg/dL)

Other than activated charcoal and cathartic, severe toxicity should be treated with antidotes (edetate calcium disodium [EDTA] and dimercaprol).


Ingestion of pesticide and industrial chemicals

Symptoms usually appear within 1 hour after ingestion but may be delayed as long as 12 hours.

Abdominal pain, watery diarrhoea, vomiting, skeletal muscle cramps, profound dehydration, and shock may occur.

Gastric lavage and activated charcoal

Dimercaprol injection 10% solution in oil (3–5 mg/kg IM q4–6h for 2 d) and oral penicillamine (100 mg/kg/d divided qid for 1 wk)

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