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Food Poisoning

Food Poisoning


Food poisoning results from ingestion of food contaminated with chemicals (insecticides, methyl alcohol), micro-organisms (bacteria, fungi, viruses, parasites, algae) or its toxins (e.g. ciguatera poisoning). It includes ingestion of food containing natural toxins (e.g. puffer fish and poisonous mushrooms) but does not include food allergies.

Causative Agents

The commonest identified bacterial pathogens causing food poisoning in Singapore are Campylobacter jejuni, Salmonella spp (non-typhoidal), Staphylococcus aureus, Vibrio parahaemolyticus, Bacillus cereus and E.coli.

Incubation Period

Varies from hours to days depending on organism and dose (see table).

Infectious Period

Generally not contagious but person-person transmission can occur with poor personal hygiene via faecal-oral transmission, if the infectious dose of the causative agent is low.


See Table.


There were 211 notifications of food poisoning involving 1599 cases in 2009 compared with 136 notifications and 1252 cases in 2008.

In December 2003/Jan 2004, 305 cases of norovirus gastroenteritis were reported in
14 separate outbreaks in different parts of Singapore. It was traced to the consumption of imported half-shelled chilled oysters.

In Nov/Dec 2007, an outbreak of 216 cases of salmonellosis caused by S. enteritidis was traced to the consumption of cream cakes produced in a factory and distributed to various retail outlets. In April 2009, there was an outbreak caused by Vibrio parahaemolyticus, which was believed to be due to cross-contamination between Indian “rojak” and raw seafood ingredients harbouring the bacteria. A total of 154 cases, including 2 deaths were reported, with 48 cases hospitalised.

The majority of foodborne diseases will present with acute gastrointestinal symptoms:

  • Vomiting (e.g. S. aureus, B. cereus).
  • Diarrhoea (e.g. Salmonella spp, enterotoxigenic E. coli).
  • Fever may or may not be present. Usually absent if due to organisms which elaborate a toxin e.g. S. aureus. The presence of fever may suggest infection with invasive bacteria (e.g. Salmonella, Shigella or Campylobacter), enteric viruses, or a cytotoxic organism such as Clostridium difficile or Entamoeba histolytica.
  • Fever, abdominal pain and diarrhoea with leucocytes or blood (e.g. Salmonella spp, Shigella spp, C. jejuni). Refer to individual chapters.
  • Post-infectious syndromes e.g. Reiter’s syndrome after salmonellosis, Guillain- Barré syndrome after campylobacteriosis, and haemolytic uremic syndrome (HUS) after infections with E. coli O157:H7.

  • Appropriate specimens for laboratory confirmation vary depending on the clinical and epidemiological features (e.g. food implicated), and the likely aetiological agent. Specimens to be obtained include:
    • Patient’s stools, vomitus and blood.
    • Food handlers’ hand, stool or nose cultures.
  • Isolation of the organism from food is preferred when diagnosing S. aureus or C. perfringens, as these bacteria are also part of the normal flora.
  • If E. coli 0157:H7 is suspected, the microbiology laboratory needs to be informed.

All food poisoning outbreaks should be notified to the Ministry of Health to facilitate investigations (MD 131 or electronically via CD-LENS). An epidemiological investigation will be conducted to determine the extent of the problem, source of infection and mode of transmission.

  • General
    • Rehydration (either oral or intravenous) remains the mainstay of therapy.
    • Most cases of food poisoning can be treated as outpatients with oral rehydration (ORS - Oral rehydration salts) and symptomatic treatment.
    • Patients with bloody diarrhoea, high fever and dehydration and failure to retain fluids should be considered for admission.
    • Anti-motility agents should be avoided as they may cause dangerous paralytic ileus and abdominal distension especially in children and infants. Loperamide or bismuth subsalicylate are safer alternatives.
    • Antimicrobial agents are of no value in the management of viral gastroenteritis, Staphylococcal, C. perfringens or B. cereus food poisoning.
    • Food poisoning caused by V. parahaemolyticus, Shiga toxin-producing, or invasive E. coli or Y. enterocolitica are usually self limiting.
    • There is no specific treatment for cryptosporidiosis.
    • Patients with E. coli O157:H7 infection should be evaluated expectantly for the development of haemolytic uremic syndrome. Antibiotic treatment is contraindicated especially in children.
  • Specific Treatment
    • Antimicrobial agents may be used in the treatment of shigellosis, cholera, invasive salmonellosis and typhoid fever, but should be avoided in uncomplicated gastrointestinal infection caused by non-typhoidal Salmonella. (See specific chapters for treatment choices).
    • Listeria monocytogenes gastroenteritis may not require antibiotic therapy but consider treatment in elderly, pregnant women and those with compromised cell-mediated immunity. Treatment with ampicillin or penicillin (drugs of choice). TMP/SMX, a carbapenem or vancomycin are alternatives. Cephalosporins are ineffective.
    • G. lamblia infection: metronidazole 250mg tds x 5-7 days. Alternative: albendazole 400mg once daily x 5 days.
    • Cyclospora infection: TMP/SMX (Bactrim) 2 tabs bd oral x 7-10 days.
    • Campylobacter jejuni infection: mostly self-limiting. Consider treatment if high fevers, prolonged or severe symptoms, bloody diarrhoea, pregnant or immunocompromised hosts. Treatment with: erythromycin 500mg qds x 5 days or azithromycin 500mg once daily x 3 days. Alternative: ciprofloxacin 500mg bd x 5 days. Increasing resistance to fluoroquinolones especially in Southeast Asia.

When an outbreak is suspected, the Ministry of Health will:

  • Conduct preliminary case investigation to obtain information on food history, onset of illness and symptoms.
  • Inspect implicated food establishments to look into external contamination (such as environmental sanitation, source of water supply, refuse disposal, toilet facilities, etc) and personal hygiene and food handling practices.
  • Sample food, vomitus and stools when available for microbiological analyses at the Department of Pathology, Singapore General Hospital and for toxicological analyses at the Health Sciences Authority, if indicated.
  • Carry out questionnaire surveys to determine the clinical symptoms, severity of illness and food-specific attack rates.
  • Refer implicated food handlers to the CDC for medical examination and stool cultures.

Causative Agent


Mode of

Clinical Features

Food Vehicle

Prevention & Control

Staphylococcus aureus

1-7 hrs

Preformed toxin

Abd cramps, N, V

Meat and dairy products

Proper food handling and storage with proper temperature control. Exclude food
handlers with septic wounds.

Bacillus cereus

1-6 hrs or
8 to 16 hours

Heat-stable toxin
Heat-labile toxin

N, V
Abd cramps, D

Fried rice, meat, vegetables

Thorough and rapid reheating of cooked food


12-36 hrs


D, abd cramps, N, V, F

Meat, poultry, eggs and dairy products

Proper meat processing; adequate cooking;
avoid cross-contamination; proper temperature control and storage.

Campylobacter jejuni

1-7 days


D, abd cramps, N, V, F

Poultry, meat and unpasteurised milk

Wash hands after contact with animal/animal products; thorough cooking and proper storage of food of animal origin;
pasteurisation of milk.

Incubation Period

Incubation Period

Mode of Action

Clinical Features

Food Vehicle

Prevention & Control

E. coli (EHEC) including E.coli 0157:H7)

3-8 days


Severe abd cramps, watery to bloody D, hemorrhagic uremic
syndrome (HUS)

Ground beef, unpasteurised milk and hamburgers

Proper processing and handling of meat; adequate cooking and storage.

Listeria monocytogenes

Variable. 1- 70
days; median 3 wks


mild flu-like illness to meningitis, meningo-encephalitis

Cold processed meat, unpasteurised milk, dairy products and vegetables

Proper processing and handling; prevent cross-contamination; adequate cooking; pasteurisation
of dairy foods.

Clostridium botulinum

18-36 hrs


V, constipation, dryness of mouth, change of voice, dysphagia, ptosis,

Home canned food

Proper supervision of home canning; adequate heating to 100°C for 10 minutes OR 80° C for 30 minutes.


12-48 hrs


N, V, D, abd cramps, transient F, myalgia

Contaminated food such as oysters and contaminated water
supply (person-person transmission can occur)

Provision of safe food and water, proper handling of cold foods, hand-washing


1-3 days


V, D, F

Contaminated food (person- person transmission can occur)

Proper handling of food, personal hygiene

Causative Agent

Incubation Period

Mode of Action

Clinical Features

Food Vehicle

Prevention & Control


1- 15days


D, N, V, abd
cramps, LOA, LOW

Contaminated food or water

Avoiding food or water that may
be contaminated with human stool

Cryptosporidium parvum

5-6 days


D, abd cramps, F, LOW, V

Water , including recreational water, contaminated by faeces
of livestock (person-person transmission can occur)

Provision of safe water supply, boiling water advised for immunodeficient persons

Giardia lamblia

1-2 wks


N, V, D, abd cramps, bloatedness, LOW,

Contaminated food and water (person-person transmission can occur)

Proper water treatment, good personal hygiene

Other viruses (astrovirus, adenovirus,

10-70 hrs


N, V, D, abd cramps, malaise, headache, F

Contaminated food, ready-to- eat food touched by infected workers, some shellfish

Good personal hygiene

Entamoeba histolytica

2 days- 4 wks


Bloody D, lower abd cramps

Food contaminated by ill food handler

Good personal hygiene

Abbreviations: N, nausea; V, vomiting; D, diarrhoea; abd, abdominal; LOW, loss of weight; LOA, loss of appetite; F, fever.




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