Notification requirement for food or water-borne illness
Two or more related cases of suspected food or water borne illness are categorised as an 'urgent' notifiable condition and must be notified by medical practitioners and pathology services immediately by telephone, whether presumptive or confirmed.
This is a Victorian statutory requirement.
Primary school and children’s services centre exclusion for food- or water-borne illness
For most gastrointestinal illnesses, children should be excluded from school or childcare until at least 24 hours after the diarrhoea has ceased.
Infectious and other causative agents of food or water-borne illness
The most frequent causes of food or water-borne illnesses are bacteria, viruses and parasites. Refer to specific sections for details on the more common agents.
Noninfective agents include:
- heavy metal poisoning, including cadmium, copper, lead, tin and zinc
- fish toxins that are present in some shellfish or fish, such as paralytic shellfish poisoning, scombroid or ciguatera
- plant toxins that occur naturally in some foods, such as toxic fungi and green potato skins
- toxic cyanobacteria (blue–green algae) overgrowth in water.
- toxin produced in food
- damage to gut wall and/or systemic infection
Vibrio cholerae/V. parahaemolyticus
- hepatitis A and E viruses
- noroviruses and other small round structured viruses (SRSVs)
Worms and nematodes include:
Identification of food or water-borne illness
Symptoms vary with the causative agent, and range from slight abdominal pain and nausea to retching, vomiting, abdominal cramps, fever and diarrhoea. Fever, chills, headache, malaise and muscular pains may accompany gastrointestinal symptoms. Vomiting, with or without diarrhoea, abdominal cramps and fever are common symptoms of viral disease or staphylococcal intoxication. Certain food-borne illnesses can present with meningitis or septicaemia (listeriosis), or with neurological symptoms (paralytic shellfish poisoning, botulism).
Severity depends on host and agent characteristics, and the infectious dose. Hospitalisation and death may occur as a result of acute dehydration, metabolic acidosis and subsequent organ failure.
The duration of illness varies from hours (24–48 hours in viral and staphylococcal infections) to days, and even weeks for salmonellosis and campylobacteriosis.
Diagnostic methods vary according to the type of infective agent:
- Bacteria can be isolated from faeces or blood, or by detection of toxin.
- Parasites and worms/nematodes can be isolated by microscopy of fresh or appropriately preserved faeces.
- Viruses can be isolated by stool electron microscopy (EM), immune EM or paired sera from patients to detect seroconversion to a virus.
- Chemicals can be isolated by serological detection of implicated compounds.
Advice regarding specific tests should be sought from laboratories with expertise in the identification of gastrointestinal pathogens and chemical agents.
Incubation period of food or water-borne illness
Incubation periods are typically short for viruses and toxin-producing bacteria, and longer for other causes.
Public health significance and occurrence of food or water-borne illness
Food and water-borne diseases are thought to be the most common of all acute illnesses. However, a large proportion of disease is not detected, as many people will not seek healthcare with mild illness. Occurrence is worldwide, and the incidence varies from country to country. In recent years, detection of outbreaks of viral origin, especially noroviruses, has been increasing.
Reservoir of food or water-borne illness
Soil, dust, cereals are reservoirs for food and water-borne illness.
For bacteria and parasites, fish, birds, reptiles, and wild and domestic mammals are reservoirs.
For viruses, humans are the reservoir.
Mode of transmission of food or water-borne illness
Transmission is predominantly via the faecal–oral route or ingestion of contaminated food and water and fomites. Airborne transmission – via fomites – has been implicated in outbreaks involving viral pathogens.
Period of communicability of food or water-borne illness
Communicable periods for food- and water-borne illnesses depend on the causative agents. Viruses are generally communicable during the acute phase and up to 2 days after recovery, whereas bacteria are generally communicable during the acute diarrhoeal stage. For parasites, refer to relevant sections in this book.
Susceptibility and resistance to food or water-borne illness
For most infections, everyone is susceptible. However, sporadic disease is more often detected in young children, the elderly or immunocompromised people. This is in some part due to the healthcare-seeking behaviours of those caring for patients in these categories.
Control measures for food or water-borne illness
Preventing contamination of potable water is very important. Contaminated water should be treated by adequate filtration and disinfection or by boiling.
Avoiding contamination of food is also important. This can be achieved by:
- providing raw materials of better microbiological quality
- educating food handlers about proper food processing, preparation and storage, and personal hygiene
- adopting the following ‘10 golden rules for safe food preparation’ developed by the World Health Organization
- Choose food processed for safety.
- Cook food thoroughly.
- Eat cooked food immediately.
- Store cooked food carefully.
- Reheat cooked food thoroughly.
- Avoid contact between raw foods and cooked foods.
- Wash hands repeatedly.
- Keep all kitchen surfaces meticulously clean.
- Protect food from insects, rodents and other animals.
- Use pure water and raw materials.
Incorporation of HACCP (hazard analysis critical control point) systems is important for good manufacturing practices for food industries.
Vaccines are currently available for cholera, rotavirus, typhoid fever and hepatitis A (refer to relevant sections).
Control of case
Control of the case ranges from supportive treatment and rehydration to hospitalisation.
Cases due to infection need exclusion from food handling, schools and children’s services centres until after the diarrhoea has ceased or two separate faecal samples over 24 hours have been negative.
Healthcare workers need exclusion if employed in an area with high-risk patients, such as special care nurseries or nursing homes, until after the diarrhoea has ceased for 48 hours.
Control of contacts
Control of contacts includes:
- prevention of further ingestion of contaminated food or water
- surveillance of contacts who are food handlers, if required
- withdrawal from sale of implicated food (if in retail outlets).
Control of environment
Control of the environment involves investigating water sources, or places of manufacture or preparation of implicated food, and instituting corrective action.
Outbreak measures for food or water-borne illness
Outbreaks of food- or water-borne illness are usually detected following the onset of illness in a group of people who have shared a common meal. The primary objectives of outbreak control are rapid identification of the causative agent through epidemiological, environmental and laboratory investigations, and prevention of further disease by destruction or denaturation of the source.
International outbreaks are increasingly being recognised, primarily due to the increased trade in food and agricultural products worldwide. Food- and water-borne pathogens and contaminants have been identified as potential biological terrorism agents. Cases of rare diseases such as botulism should be investigated immediately. Some diseases, such as cholera, require notification to the World Health Organization.
Quarantine of suspected sources or halting of international trade should be coordinated through Food Standards Australia New Zealand.