Norovirus infection

Noroviruses are a frequent cause of viral gastroenteritis in individuals of all ages worldwide. Transmission commonly occurs from person to person, as well as through contact with contaminated surfaces, food, and water. The clinical presentation of norovirus infection includes acute-onset vomiting and watery diarrhea. If classic clinical features of norovirus are present, treatment can usually be given without diagnostic confirmation; however, viral studies are recommended in certain cases, e.g., severe gastroenteritis, suspected outbreaks. Treatment is typically supportive (e.g., treatment of dehydration) as the condition normally self-resolves within 72 hours. Given its virulence and short incubation period, norovirus infection may quickly lead to outbreaks, which must be reported.

• Peak incidence: November–March (winter months)
• Community outbreaks (in nursing homes, hospitals, preschools, cruise ships, etc.) are common.
• Older and immunocompromised patients are commonly affected.
• Most common cause of:
  • Adult gastroenteritis
  • Severe acute gastroenteritis in children younger than 5 years of age
  • Foodborne illness

References:^[1][2][3]

Epidemiological data refers to the US, unless otherwise specified.

• Pathogen: Norovirus; is a non‑enveloped RNA calicivirus.
• Transmission
  • Fecal‑oral route through contaminated food or water, person‑to‑person contact, via airborne droplets, and contact with contaminated surfaces
  • The virus is highly virulent.
  • Individuals are highly infectious during the acute phase and 24–72 hours following onset of symptoms

Viral pathogens in gastroenteritis (Rotavirus is a Reovirus, Norovirus is a Calicivirus): Rotate Reo, the calico cat off to Norway!

References:^[4]

• Incubation period: 12–48 hours
• Nausea and acute-onset vomiting
• Watery, non-bloody diarrhea
• Abdominal cramps
• Fever
• Symptoms resolve after 48–72 hours.

Overview ^[5][6]

• Diagnosis is usually clinical; diagnostic studies are not required because confirmation does not affect management.
• Consider diagnostic studies in the following: ^[5][6]
  • Patients with red flags for diarrhea or risk factors for severe infection
  • Diagnostic uncertainty
  • Concern for community or institutional outbreaks (see “Prevention”)

Suspect a possible norovirus outbreak if ≥ 2 patients with an epidemiological link present with symptoms of gastroenteritis within the same timeframe. ^[7]

Laboratory studies ^[3][8][9]

• Viral studies for norovirus: usually performed on whole stool ^[3]
  • Reverse transcription-quantitative PCR (RT-qPCR): preferred
  • Multiplex assays: allow for detection of multiple pathogens
  • Others (not routinely used in clinical practice): e.g., enzyme immunoassays, genotyping
• Additional studies
  • Diagnostic uncertainty: Perform diagnostic studies for infectious gastroenteritis.
  • Signs of significant dehydration: Perform diagnostic studies for dehydration.

Whole stool is the preferred sample for viral testing. ^[3]

• Rotavirus infection
• Bacterial gastroenteritis
• Food poisoning

References:^[10]

The differential diagnoses listed here are not exhaustive.

• Treatment is supportive (e.g., fluid replacement, electrolyte repletion, antiemetics). ^[5][6][11]
  • Children: See “Treatment of infectious gastroenteritis in children.”
  • Adults: See “Supportive therapy for gastroenteritis.”
• Patients with severe gastroenteritis or signs of significant dehydration may require inpatient treatment, including IV fluid resuscitation. ^[5][6][11]
• Nitazoxanide may reduce the duration of illness, but evidence supporting its use is limited. ^[12]
• For outpatients, educate patients and/or caregivers on:
  • The expected duration of illness
  • Return precautions
  • Prevention of norovirus transmission

Adults aged > 65 years are at increased risk for complications (e.g., dehydration, prolonged symptom duration) and thus more likely to require hospital admission. ^[13]

Prevention of norovirus transmission ^[3][7]

• Educate patients and/or caregivers on preventing onward transmission of gastroenteritis.
• Because of the risk of ongoing viral shedding, patients should for at least 48–72 hours after symptoms have resolved:
  • Isolate at home ^[14]
  • Avoid preparing food for others

Identification and management of outbreaks ^[3][7][14]

Norovirus is the most common cause of gastroenteritis outbreaks, which can be contained by early identification and management. ^[7]

• Consider a possible outbreak if:
  • > 2 linked patients (e.g., travel on the same cruise ship, use of the same community pool) present with symptoms of gastroenteritis
  • Patients present with symptoms within 1–2 days of each other
• Confirmation of norovirus
  • Viral studies including genotyping (see “Diagnostics of norovirus”) ^[8][9][15]
  • If viral studies are not possible, consider using the Kaplan criteria; norovirus is likely if: ^[7][14]
    • The mean or median duration of disease is 12–60 hours after an incubation period of 24–48 hours
    • More than 50% of affected patients have vomiting
    • No enteric bacteria have been detected.
• Report all suspected outbreaks to the local health department.
• Institutional outbreaks: See also “Infection prevention and control.” ^[14]
  • Start isolation precautions.
    • Use personal protective equipment (gown, gloves, face mask)
    • Maintain contact precautions until patients are asymptomatic for 48 hours.
  • Increase the frequency of cleaning.
  • Encourage soap and water for hand hygiene as opposed to alcohol-based hand sanitizers. ^[3][6][7]
  • Reduce the risk of iatrogenic spread by:
    • Allocating staff to cohorts and preventing movement between patient cohorts
    • Ensuring infected staff do not return to work until at least 48 hours after resolution of symptoms
    • Suspending group activities
    • Prohibiting nonessential staff, visitors, and volunteers from affected areas

Norovirus can be transmitted via food, water, or from person to person, making it extremely contagious. Report all suspected outbreaks to local health departments. ^[3]

If food or water is suspected as the source of an outbreak, collect a specimen and contact local health authorities for further instructions. ^[3][16]