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Listeriosis (Invasive)

Queensland Health Guidelines for Public Health Units

Revision History

Version Date Changes
1.0 April 2010  Full revision of guideline. 

Infectious Agent

The agent is Listeria monocytogenes. Human infections are usually caused by serotypes 1/2a, 1/2b, 1/2c and 4b.

Notification Criteria

Laboratory definitive evidence:
Isolation or detection of Listeria monocytogenes from a site that is normally sterile, including foetal gastrointestinal contents.

Community Outbreak Criteria:
Two or more associated cases other than maternal and foetal.

Notification Procedure

Pathology Laboratories

To notify on confirmation of diagnosis by telephone or facsimile.

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Lab Aspects

Faecal, blood or CSF cultures as appropriate. Molecular serotyping and genotyping of human isolates may aid in the detection of outbreaks. Additional typing is recommended for further characterisation of isolates during outbreak investigations.

Reporting to NOCS

Report only confirmed cases.

Confirmed case: A confirmed case requires laboratory definitive evidence from blood, cerebrospinal fluid or other normally sterile sites, including foetal gastrointestinal contents.

Where a mother and foetus/neonate are both laboratory confirmed, cases should be notified as follows:

  1. For notifications in foetuses <20 weeks, create a single notification (ie. under mother's name).
  2. For notifications in foetuses 20 weeks or over, create notifications for both child and mother.

Objectives of Surveillance:                                 
• To monitor the epidemiology of listeriosis and to inform public health initiatives.
• To detect outbreaks of disease, so as to enable prompt public health responses.

Public Health Significance and Occurrence

Invasive listeriosis is an uncommon disease in humans. In Australia between 2002-2006, the mean notification rate was 0.3 infections per 100,000.

Typically listeriosis occurs sporadically. However, several outbreaks have been documented, including an outbreak in Australia in 2009 associated with pre-packaged food containing contaminated chicken. Those at highest risk are neonates, older people, immuno-compromised individuals, pregnant women and alcoholic, cirrhotic or diabetic adults.  Asymptomatic infections probably occur at all ages, although these are of importance only during pregnancy, because of the risk of foetal loss. Infants may be stillborn, born with septicaemia, or develop meningitis in the neonatal period, even though the mother may be asymptomatic at delivery. The postpartum course of the mother is usually uneventful, but the case-fatality rate is 30% in newborn infants, and approaches 50% when onset occurs in the first 4 days. The overall case-fatality rate among non-pregnant adults has been reported to be up to 30%, with the case-fatality rate higher among patients aged 50 years and older than in other age groups.

Clinical Features

A bacterial infection that usually causes a mild febrile illness, but can progress to meningoencephalitis and/or septicaemia in newborns and adults. In pregnant women infection can cause abortion, preterm delivery and foetal infection. Those at highest risk are neonates, older people, immunocompromised individuals, pregnant women and alcoholic, cirrhotic or diabetic adults. Non-pregnant adults frequently present with sepsis, meningitis, or meningo-encephalitis. Focal infections such as pneumonia, endocarditis, infected prosthetic joints, localised internal abscesses and granulomatous lesions in the liver and other organs have been described. The onset of meningoencephalitis (which is rare in pregnant women) may be sudden, with fever, intense headache, nausea, vomiting and signs of meningeal irritation, or may be subacute, particularly in an immunocompromised or elderly host. Delirium and coma may appear early; occasionally there is collapse and shock.

The normal host who acquires infection may exhibit only an acute, mild, and non-specific illness with symptoms such as fever, headache, myalgia and gastrointestinal symptoms. This may be especially dangerous in pregnant women who transfer the infection to the foetus, which can result in stillbirth or premature birth. Babies may be severely affected with conditions such as septicaemia and meningitis (early-onset neonatal listeriosis).

Late onset neonatal listeriosis (usually presenting as purulent meningitis) generally affects full-term babies who are usually healthy at birth. The onset of symptoms in these babies occurs several days to weeks after birth (a mean of 14 days), possibly as a result of infection acquired from the mother's genital tract during delivery or postnatally through cross-infection.

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Reservoir

Listeria is widespread in the environment.  Listeria monocytogenes is carried in the gastrointestinal tract of many species of both domesticated and wild animals.  It has also been detected in birds, frogs, fish and crustaceans. Asymptomatic faecal carriage is uncommon in humans (1% to 5%). It is a common environmental contaminant found in soil, surface water, decomposing organic matter, spoiled silage, sewage, industrial food-processing environments and raw foods including vegetables, meats and dairy products.

Listeria monocytogenes can survive and grow over a wide range of environmental conditions such as refrigeration temperatures (including the ability to survive freezing), low pH and high salt concentration. The wide environmental conditions under which it can grow, including growth under refrigeration, make control of the organism in foods by methods relying on refrigeration extremely difficult.

Mode of Transmission

Primarily a foodborne disease transmitted by ingestion of contaminated food such as raw milk, soft cheeses, other dairy products, vegetables/salads, shellfish, pate, and ready to eat processed (eg. delicatessen) meats. Infected cutaneous lesions on hands and arms have been reported among veterinarians and farm workers following direct contact with diseased animals. In neonatal infections, the organism can be transmitted from mother to foetus in utero or during passage through the infected birth canal. Nursery outbreaks attributed to contaminated equipment or materials have occurred rarely.

Incubation Period

Not well established and variable, ranging from 3-70 days with median estimated to be 3 weeks.

For non-invasive febrile gastroenteritis, median incubation period is 24 hours (range 6 hours – 10 days).

Period of Communicability

Mothers of infected newborns may shed the infectious agent in vaginal discharges and urine for 7-10 days after delivery, rarely longer. Infected individuals can shed the organisms in their stools for several months.

Susceptibility and Resistance

Those at highest risk of infection are neonates, older people, immunocompromised persons and pregnant women. Foetuses and newborn infants are highly susceptible. There is a strong association between decreased immunity (particularly cell-mediated) and invasive listeriosis, and disease is frequently superimposed on other debilitating illnesses such as cancer, organ transplantation, diabetes, chronic renal disease, cirrhosis, heart disease, HIV infection and in those on corticosteroids. In immunocompetent hosts, Listeria may be more likely to manifest as febrile gastroenteritis. There is little evidence of acquired immunity, even after prolonged severe infection.

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Management

Cases:

  • Investigation:  Investigate all cases. Attempt to identify potential food source. If a food source is suspected/identified, inform environmental health services within the public health unit.  Ensure case isolates are forwarded to Forensic and Scientific Services Public Health Microbiology Laboratory for serotyping and genotyping. Email or fax case report forms to OzFoodNet to facilitate identification of multi-jurisdictional clusters.


  • Restriction:  None


  • Treatment: Cases should be treated with appropriate antibiotics.
     For treatment regimens refer to the current edition of the Therapeutic Guidelines: Antibiotic.


  • Counselling: The case should be advised of the nature of the infection and its mode of transmission, and to avoid contact with pregnant women, neonates and known immunocompromised persons during the illness.  Asymptomatic mothers of neonatal cases can shed the organism for up to 10 days after delivery, and should be advised to practise good hand washing procedures. Cases should be educated about the foods that are at higher risk of being contaminated and about safe food handling and storage.

Contacts:

  • Contact Tracing:  No.

Community outbreaks/epidemics:

If two or more cases are epidemiologically linked eg. common food source or common setting, or microbiologically linked (by genotyping) then convene the outbreak control team. Investigation should include the following:

  • Look for common source of infection.
  • Test any available suspected foods.
  • Further characterisation of isolates should be performed to confirm the outbreak and demonstrate whether case isolates and food isolates are indistinguishable.
  • Investigate the source of any foods found to be positive for L. monocytogenes to determine at what point they became contaminated.
  • Recall contaminated food if necessary.
  • Educate those at risk on high risk foods.
  • Educate on appropriate food handling and storage.
  • Educate on good hygiene and hand washing procedures.

In some outbreak settings, active case finding and investigation of non-invasive listeriosis (such as acute febrile gastroenteritis) may be warranted.

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Preventive Measures

Pregnant women and immunocompromised individuals should:

  • eat only properly cooked meats and pasteurised dairy products. Avoid eating all soft cheeses, pate, cold delicatessen meats, pre-prepared or stored salads, raw seafood and smoked seafood
  • thoroughly wash raw vegetables and salads before eating
  • avoid contamination of cooked or ready-to-eat foods by raw meats or unwashed vegetables (eg. by using different cutting boards, high standards of hygiene, etc)
  • also avoid contact with sick animals.

Food handlers in retail food establishments, particularly delicatessens and take away food premises, should be educated on appropriate food handling and storage procedures.

Summary

For community outbreaks, prepare an outbreak summary report of the investigation for the Communicable Diseases Branch, Queensland Health, on request.

References

Heymann, D. (Ed).  2008. Control of Communicable Diseases Manual, 19th edition.  American Public Health Association: Washington.

Centers for Disease Control.  2004.  Diagnosis and management of foodborne illnesses – a primer for physicians and other health care professionals.  Morbidity and Mortality Weekly Review 53 (RR-4):1-35.

Mandell GL, Bennett JE, Dolin R (eds). 2009. Principles and Practice of Infectious Diseases, 7th edition.  Churchill Livingstone, Philadelphia.

The OzFoodNet Working Group. 2008. Monitoring the incidence and causes of diseases potentially transmitted by food in Australia: Annual report of the OzFoodNet Network, 2007. Communicable Diseases Intelligence 32 (4).

Kliegman RD, Behrmann RE, Jenson HB, Stanton BF. 2007. Nelson Textbook of Pediatrics 18th edition. Saunders Elsevier: Philadelphia.

Gandhi M, Chikindas ML. 2007. Listeria: A foodborne pathogen that knows how to survive. Int J Food Microbiol. 113(1): 1-15.

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Last updated: 9 September 2010