Listeria monocytogenes

Diagnosis

Indications for Testing

  • High level of suspicion coupled with symptoms in at-risk patients

Laboratory Testing

  • Rapid detection tests may be available (monoclonal antibodies or nucleic acid hybridization) but may only identify genus Listeria
  • Culture (blood, CSF, amniotic fluid, maternal/fetal tissues)

Differential Diagnosis

Clinical Background

Listeria monocytogenes is the causative agent of Listeriosis and is transmitted through contaminated foods. Listeriosis is a virulent foodborne illness with 20-30% mortality, especially in immunocompromised individuals.

Epidemiology

  • Incidence – 1-6/1,000,000
  • Transmission – food-borne from contaminated milk and dairy products, various meats, fresh produce

Organism

  • Gram-positive facultative, intracellular rods
  • Hardy organism – capable of growing at both 4ºC and 37ºC
  • Organisms are motile by means of flagella at room temperature, but not at 37ºC (body temperature); can spread from cell to cell via actin polymerization
  • L. monocytogenes is the only recognized human pathogen in Listeria species and has >14 serotypes

Risk Factors

Clinical Presentation

  • Initial symptoms – typically fever, muscle aches, nausea, diarrhea
  • Localized infection
    • Skin
    • Intra-abdominal
  • More serious symptoms may develop if infection spreads
  • Manifestations in pregnancy

Prevention

  • Cook meats thoroughly 
  • Wash raw vegetables
  • Avoid unpasteurized milk or foods made from unpasteurized milk (soft cheeses are a particular problem)

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Cerebrospinal Fluid (CSF) Culture and Gram Stain 0060106
Method: Stain/Culture/Identification

Identify Listeria as agent of meningitis

    
Blood Culture 0060102
Method: Continuous Monitoring Blood Culture/Identification

Identify Listeria as agent of infection

Testing is limited to the University of Utah Health Sciences Center only

  
Body Fluid Culture and Gram Stain 0060108
Method: Stain/Culture/Identification

Identify Listeria as agent of infection

    
Listeria Antibody, Serum by CF 0099529
Method: Semi-Quantitative Complement Fixation

Confirm Listeria as agent of infection (endocarditis, CNS)

Document past infection if culture was not performed or if patient received antibiotics that would make culture unreliable

    
Listeria Antibody, CSF by CF 2002086
Method: Semi-Quantitative Complement Fixation

Confirm Listeria as agent of infection (CNS)

Document past infection if culture was not performed or if patient received antibiotics that would make culture unreliable