Background

• leading cause of both sporadic and epidemic gastroenteritis worldwide

  
  • non-enveloped RNA virus

  • genotype GII.4 associated with majority of global outbreaks since mid-1990s but new pandemic strains emerge every 2 to 4 years

  • reported to cause about 50% of epidemic gastroenteritis and >90% of nonbacterial epidemic gastroenteritis

• estimated at 21 million cases, >70,000 hospitalizations, and 800 deaths annually across all age groups 

• most common viral cause of traveler’s diarrhea

• important cause of traveler’s diarrhea in Latin America and Africa 

• Highly contagious due to 

  
  • low infectious dose (as few as 18 viral particles)

  • environmental stability able to withstand temperatures from 0° to 60° C (32° to 140° F)

  • survives up to 10 parts per million chlorine

  • stable for long periods (up to 2 weeks) on environmental surfaces, which may act as a reservoir during outbreaks

  • in water, virus able to infect human volunteers after 2 months and intact viral capsid detected after 3 years

  • multiple potential routes of transmission

• Fecal-oral transmission is main means of spread, but may also be transmitted from person to person, via fomites or aerosolized from vomitus. 

• Short incubation period from time of exposure to infection (typically 24 to 48 hours).

• Peak incidence typically occurs in winter months in temperate climates

• Risk factors

  
  • Proximity to infected persons (primary risk factor) with outbreaks often occurring in
    • cruise ships

    • healthcare settings

    • child care centers

    • nursing homes

    • hotels or other food service locations

  • Ingestion of contaminated food or water associated with infection, particularly
    • raw shellfish

    • prepared foods

    • recreational water facilities

• Immunocompromised patients may be predisposed to severe or prolonged disease


Evaluation


• Classic clinical presentation 

  
  • acute-onset vomiting (may be projectile)

  • non-bloody diarrhea

  • short-lived fever (<50% )

• Most pathologic changes found in proximal jejunum

• Examination

  
  • Assess for signs of dehydration

  • Abdominal examination usually benign


Diagnosis


• suspect norovirus gastroenteritis in patients with acute onset nausea, vomiting, and diarrhea

• laboratory testing not needed in most cases as illness is often self-limited

• when laboratory confirmation needed, such as in cases of severe or prolonged illness, options for testing stool include

  
  • real-time reverse transcription polymerase chain reaction (RT-PCR)
    • test of choice (not available in all areas)

    • high sensitivity and specificity

    • stool antigen testing (immunoassays)

    • low sensitivity, often genotype-dependent (negative outbreaks should be assessed with RT-PCR)

    • high specificity 

  • multiplex assays for simultaneously detecting multiple enteric pathogens are in development

• Kaplan criteria 

  
  • may aid in distinguishing norovirus from other causes of gastroenteritis in outbreak settings when laboratory confirmation is not possible

  • presence of all 4 of the following features has high-positive predictive value during an outbreak
    • mean or median incubation period 24 to 48 hours

    • mean or median duration of illness 12 to 60 hours

    • ≥50% cases having vomiting

    • stool culture negative for bacterial and parasitic pathogens

• Immunity short-lived


From the February 01, 2016 Issue of Clinical Advisor