Acute gastroenteritis is one of the most common diseases in humans. Viral agents are an important cause of diarrheal illness. The two most common viral agents are:

• Norovirus (Norwalk-like virus)
• Rotavirus

Norovirus

Epidemiology

• Leading cause of nonbacterial gastroenteritis worldwide; genogroups I and II account for approximately 99% of Norovirus infections in humans
• In the U.S., Norovirus causes millions of infections annually, with outbreaks commonly occurring in all age groups and in varied situations such as:
  • Cruise ships
  • Restaurants (salad bars)
  • Schools
  • Healthcare facilities 
• Norovirus has a characteristically low infectious dose and can survive relatively high levels of disinfectants and varying temperatures, all of which facilitate its transmission
  • Transmission occurs mainly through the fecal-oral route by ingestion of contaminated food (eg, shellfish) or water, but can be airborne (in vomitus)

Organism

• Norovirus, formerly known as Norwalk-like virus, is a member of the Caliciviridae family
• Single-stranded RNA virus

Clinical Presentation

• Usually mild or self-limiting disease but shows high transmission rates (often greater than or equal to 30%) among contacts of infected patients
• Most common symptoms - acute onset diarrhea and vomiting with abdominal cramps, nausea, fever and headache
• Symptoms occur within 24-48 hours of infection and can range from 12-60 hours in duration
• A cause of chronic diarrhea in transplant patients
  • Symptoms in small bowel transplant patients resemble allograft rejection

Treatment

• Supportive care, as infection is self-limited
• Infection control measures are important in limiting the spread in hospital settings

Prevention

• Hygiene/handwashing, disinfection of contaminated surfaces

Rotavirus

Epidemiology

• Most important cause of severe dehydrating diarrhea in children ages 5 and younger
• Rotavirus Type A is responsible for 25-60% of severe infantile diarrhea worldwide
• Transmission is via fecal-oral route
• Nearly all children have circulating antibodies by ages 2-3 (universal infection)

Organism

• Double-stranded RNA virus

Clinical Presentation

• Varies from asymptomatic to severe dehydration and death
• Mild fever and emesis for 2-3 days
• 3-5 days of watery diarrhea following fever
• Severe and prolonged disease may occur in patients with:
  • Significant malnutrition
  • Immune deficiencies
  • Other disease such as diabetes mellitus, congenital heart disease or pulmonary disease
  • May involve extra-intestinal sites (central nervous system, liver, spleen, kidney), especially in immunocompromised children

Treatment

• Supportive care

Prevention

• Handwashing and vaccination

Norovirus

Diagnosis

• Indications for testing
  • Prolonged diarrhea or epidemic setting
  • Most norovirus diagnoses are based on clinical presentation
• Laboratory testing
  • Reverse transcription polymerase chain reaction (RT-PCR) detection for genogroups I and II - preferred test
  • EIA (antigen detection) - not as sensitive as PCR
  • Electron microscopy - insensitive test and lab specific

Rotavirus

Diagnosis

• Indications for testing - severe nonresolving diarrhea, epidemic settings, immunocompromised patient
  • Most rotovirus diarrhea is diagnosed by clinical presentation alone
• Laboratory testing
  • RT/PCR most sensitive
  • EIA (antigen detection) - acceptable sensitivity for organism
  • Electron microscopy - least sensitive and lab specific