1. Home
2. Publications & Resources
3. Control Guidelines
4. LISTERIOSIS

Control Guideline

Last updated: 01 July 2012

1. Reason for surveillance

• To identify and control the source
• To monitor the epidemiology and inform better prevention strategies.

2. Case definition

A confirmed case requires laboratory definitive evidence only.

Laboratory definitive evidence

• Isolation or detection of Listeria monocytogenes from a site that is normally sterile, including foetal gastrointestinal contents.

Clinical evidence
Not applicable

Epidemiological evidence
Not applicable

3. Notification criteria and procedure

Listeriosis is to be notified by:

• Laboratories (ideal reporting by telephone on same day of diagnosis).

Only confirmed cases should be entered onto NCIMS.

4. The disease

Infectious agent
The Gram-positive rod Listeria monocytogenes.

Mode of transmission
Neonatal infection is transmitted in utero, or via the birth canal. Listeria infection occurring after birth is usually caused by ingesting contaminated food. Some foods with an increased risk of contamination are:

• Uncooked fermented meat products
• Meat products and poultry which have not been properly cooked (≥75°C for 1 minute throughout)
• Delicatessen meats, precooked chicken and pate
• Perishable food including salads or fruit salads stored for >24 hours
• Raw fish or oysters, smoked fish or oysters
• Soft cheeses such as brie, camembert and ricotta
• Unpasteurised milk and milk products
• Raw fruiut and vegetables which have not been properly washed
• Sprouted seeds.

Rarely, contact with contaminated equipment in neonatal nurseries, or with animals and animal waste is associated with transmission.

Timeline
The typical incubation period can vary from 3 to 70 days, with a median of three weeks. During pregnancy, the foetus is infected within a few days of the mother's infection.

Infected mothers of newborn babies may shed the microorganism in vaginal discharges and urine for 7 to 10 days after delivery. Infected persons may shed the organism in the stools for several months.

Clinical presentation
Listeriosis usually presents as meningoencephalitis and/or septicaemia in newborns and adults and abortion in pregnant women. Although healthy people can be infected, the disease generally affects:

• Pregnant women
• Neonates and infants
• The frail elderly
• Immunocompromised persons, for example those with HIV/AIDS, cancer, chronic renal disease or chronic liver disease, diabetics, and those on immunosuppresive medication.

Outbreaks of food-borne listeriosis have been reported and are characterised by malaise, headache, mild fever and diarrhoea (which is not necessarily prominent). Diagnosis can often be confirmed by isolation of L. monocytogenes using special media.

5. Managing single notifications

Response times
Investigation
Within one working day of notification of a confirmed case begin follow-up investigation.

Data entry
Within 1 working day of notification enter confirmed cases on NCIMS. Where a mother and foetus/neonate are both confirmed, both cases should be reported and entered separately.

Response procedure
The response to a notification will normally be carried out in collaboration with the case's health carers. Regardless of who does the follow-up, PHU staff should interview the case with the questionnaire from the NSW health website at http://www.health.nsw.gov.au/resources/publichealth/infectious/diseases/Enteric/listeria_questionnaire_final050510.pdf and ensure that action has been taken to:

• Confirm the onset date and symptoms of the illness
• Confirm results of relevant pathology tests, or recommend the tests be done
• Find out if the case or relevant care-giver has been told what the diagnosis is before beginning the interview
• Seek the doctor's permission to contact the case or relevant care-giver
• Review case and contact management
• Ensure that all clinical isolates are sent to ICPMR for conformation and further typing
• Identify possible sources of infection.

Notify Communicable Diseases Branch by email or phone on the day of notification.

Case management
Investigation and treatment
Refer to Therapeutic Guidelines: Antibiotic for treatment options.
In a cluster, contact Communicable Diseases Branch to discuss the investigation.

Education
The case or relevant care-giver should be informed about the nature of the infection and the mode of transmission. Emphasise the importance of avoiding high-risk food.

Isolation and restriction
Isolation of cases is not necessary, provided good hygiene is observed.

Environmental evaluation
Single case notifications in persons who have eaten food at a health care facility during the incubation period should prompt referral to the NSW Food Authority for a review of that facility's food handling procedures.

Food service managers in NSW Health facilities will routinely test food samples for Listeria and are required to notify their local PHU and the NSW Food Authority if L. monocytogenes is detected in food. Food isn't sterile and Listeria bacteria are commonly found in food without ever causing harm. No action is required by the PHU unless there is a related case, or the food was ready-to-eat and served to patients. If there is reason to believe that a food contaminated with L. monocytogenes was served to inpatients who are at higher risk for disease because of 1. underlying immune suppression or 2. pregnancy then the PHU should contact relevant clinicians e.g., oncologists, immunologists and obstetricians, to inform them of the incident and remind them to consider listeriosis as a diagnosis in patients with consistent symptoms. Because there is no specific preventative action for people already exposed, direct contact with the patients is not useful.
Where a source is suspected to have caused illness on epidemiological grounds, the NSW Food Authority should be engaged to collect samples of residual food for laboratory analysis, and to provide advice and remedial actions, including assessment of potential sources of food contamination and steps taken to prevent further occurrences if possible.

Contact management
Identification of contacts
Not applicable