Food or water-borne Illness

Infectious agent:

The most frequent causes of food or water-borne illnesses are various bacteria, viruses and parasites. Refer to specific sections for detail on the more common agents. Non-infective agents:

• heavy metal poisoning, including, cadmium, copper, lead, tin and zinc

• fish toxins that are present in some shellfish or fish like paralytic shellfish poisoning or ciguatera

• plant toxins which occur naturally in some foods such as toxic fungi and green potato skins

• toxic cyanobacteria (blue green algae) overgrowth in water. Bacteria:

• toxin produced in food:

– Staphylococcus aureus

– Clostridium botulinum

– Bacillus cereus

• damage to gut wall and/or systemic infection:

– Salmonella spp.

– Shigella spp. – Clostridium perfringens

– Campylobacter spp.

– E. coli.

– Helicobacter pylori

– Vibrio cholerae/V. parahaemolyticus

– Yersinia enterocolitica

– S.typhi/Paratyphi

– Brucella spp.

– Listeria monocytogenes

Viruses:

• Hepatitis A and E viruses

• Noroviruses and other small round

structured viruses (SRSV)

• Rotavirus

Parasites:

• Cryptosporidium spp.

• Entamoeba histolytica

• Giardia lamblia

Identification:

Clinical features :

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 foodborne

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 due to 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 in salmonellosis and campylobacteriosis.

Method of diagnosis:

Diagnostic methods vary according to the type of infective agent:

• bacteria can be isolated from faeces or blood or by detection of toxin

• parasites 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:

Incubation periods are typically short for toxin-producing bacteria and longer for others.

Public health significance and occurrence:

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 health care with mild illness. Occurrence is worldwide and the incidence varies from country to country. In recent years the detection of outbreaks of viral origin, especially noroviruses, has been increasing.

Reservoir:

• Soil, dust, cereals

• Bacteria and parasites: fish, birds, reptiles, wild and domestic animals

• Viruses: humans

Mode of transmission:

Transmission is predominantly via the faecal-oral route or ingestion of contaminated food and water sources. Transmission via aerosols (produced during profuse vomiting) has been implicated in outbreaks involving viral pathogens.

Period of communicability:

Communicable periods for food and water-borne illnesses depend on the causative agents. Viruses are generally communicable during the acute phase and up to two days after recovery while bacteria are generally communicable during the acute diarrhoeal stage. For parasites refer to relevant sections in this

book.

Susceptibility and resistance:

With 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 health care seeking behaviours of those caring for patients in these categories.

Control measures:

Preventive measures:

Prevention of the 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, storage and in personal hygiene

• adopting the following ‘Ten golden rules for safe food preparation’ developed by WHO:

– 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

Incorporation of HACCP (Hazard Analysis Critical Control Point) systems is important for good  manufacturing practices for food industries. Vaccines are currently available for cholera 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. Health care 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.

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 of implicated food (if in retail outlets) from sale.

Control of environment:

Investigate water sources or place of manufacture or preparation of incriminated food and institute corrective action.

Outbreak measures:

Food and water-borne outbreaks 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 the rapid identification of the causative agent through epidemiological, environmental and laboratory investigations and prevention of further disease by destruction or denaturation of the

source.

sources of information

Food Standards Australia New Zealand,

·         http://www.foodstandards.gov.au

·         The blue book: Guidelines for the control of infectious diseases