Causative Agent
Listeriosis is caused by a bacterium named Listeria monocytogenes which is commonly
found in natural environment (e.g. soil or water). The bacterium may also be found
in some contaminated raw foods, such as unpasteurized milk, vegetables and uncooked
meats, as well as in processed foods that become contaminated during or after
processing, such as soft cheese and cold cuts.
Clinical Features
A person with listeriosis usually presents with fever, headache, and sometimes
gastrointestinal symptoms such as nausea, vomiting and diarrhoea. Some patients
may develop meningoencephalitis or septicaemia. Pregnant women, newborns/infants,
elderly and persons with chronic diseases or weakened immunity are at higher
risk of being infected. Infected pregnant mother may transmit the infection
to her foetus resulting in miscarriage or stillbirth, or her newborn resulting
in septicaemia or meningitis.
Mode of transmission
Listeriosis is mainly caused by consumption of contaminated food or transmitted
through placenta from mother to foetus or through an infected birth canal to
her newborn.
Incubation period
The incubation period may range from 3 to 70 days. On average symptoms occur
3 weeks after exposure to the bacteria.
Management
Patients with listeriosis often require hospitalisation and antibiotic is used
to treat the infection.
Prevention
Listeria monocytogenes are rather unique in the sense that they can multiply
in low temperature refrigerated foods that are contaminated but they can be
easily killed by normal cooking temperature. To prevent listeriosis, you should
maintain good personal, food and environmental hygiene.
Personal hygiene
- Wash hands properly with soap and water before eating or handling food, and
after toilet or changing diapers.
Food hygiene
1) Choose safe food
- High risk individuals such as pregnant women and persons with weakened immunity
should avoid high risk food, e.g. unpasteurised milk, soft cheese, prepared
or stored salads, and cold meats.
- Check whether food package is intact and the expiry date is not due before
purchase and consumption.
2) Cook food thoroughly
- Consume food as soon as it is done.
- Handle raw food and cooked food separately. Use separate knives and chopping
boards for each to avoid cross-contamination.
- Do not handle ready-to-eat food with bare hands; wear gloves if necessary
3) Store food properly
- Clean and defrost the refrigerator regularly and keep the temperature at or
below 4oC.
- Cover and store perishable food in refrigerator.
- Store raw and cooked food separately (upper compartment of the refrigerator
for cooked food and lower compartment for raw food) to avoid cross-contamination.
- If necessary to keep leftover food, cover and refrigerate it properly, and
consume it as soon as possible. Inspect the food before reheating; reheat thoroughly
before consumption
- Discard addled food items.
Environmental hygiene
- Keep the premises and kitchen utensils clean.
- Dispose rubbish properly.
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