Norovirus (vomiting bug)

Introduction
Norovirus is a highly contagious, non-enveloped, single-stranded RNA virus from the Caliciviridae family. It is the leading cause of acute viral gastroenteritis worldwide, affecting all age groups. The infection is commonly associated with outbreaks in closed or semi-closed environments such as schools, cruise ships, hospitals, and nursing homes. Transmission occurs primarily via the fecal–oral route, through contaminated food, water, surfaces, or direct person-to-person contact.

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Epidemiology

• Responsible for an estimated 685 million cases of acute gastroenteritis annually worldwide.

• Affects both developed and developing countries.

• Outbreaks are more common in winter in temperate climates but can occur year-round.

• Incubation period: 12–48 hours.

• Infectious dose: as few as 18 viral particles.

• Immunity after infection is short-lived, often lasting only a few months.

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Etiology and Virology

• Norovirus is genetically diverse, classified into multiple genogroups (GI–GVI).

• GI, GII, and GIV infect humans; GII.4 strains are most frequently associated with epidemics.

• The virus is stable in the environment and resistant to many disinfectants, making it highly persistent.

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Transmission

• Fecal–oral route via ingestion of contaminated food or water.

• Person-to-person spread through direct contact.

• Aerosolized particles generated during vomiting.

• Contaminated fomites (e.g., door handles, utensils).

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Pathophysiology
Norovirus infects the small intestine, causing blunting of villi, crypt cell hyperplasia, and mild inflammation without destruction of the intestinal epithelium. This leads to:

• Malabsorption of water and nutrients.

• Hypersecretion of water and electrolytes into the intestinal lumen.

• Gastrointestinal symptoms due to altered motility and stimulation of the enteric nervous system.

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Clinical Presentation

Onset: Sudden, within 1–2 days after exposure.
Symptoms:

• Nausea.

• Vomiting (more prominent in children).

• Watery, non-bloody diarrhea (more common in adults).

• Abdominal cramps.

• Low-grade fever.

• Myalgia and malaise.
  Duration: Symptoms typically resolve within 1–3 days in healthy individuals, but prolonged illness may occur in young children, older adults, and immunocompromised patients.

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Complications

• Dehydration (especially in young children and older adults).

• Electrolyte imbalances (hyponatremia, hypokalemia).

• Rare: acute kidney injury due to severe dehydration.

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Diagnosis

Clinical diagnosis: Often based on characteristic symptoms and outbreak context.
Laboratory confirmation:

• Reverse transcription-polymerase chain reaction (RT-PCR): gold standard.

• Enzyme immunoassays (EIAs) for antigen detection (less sensitive).
  Stool cultures are negative for bacterial pathogens in pure viral gastroenteritis.

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Management

General principles: There is no specific antiviral therapy; treatment is supportive.

1. Rehydration

• Oral rehydration solution (ORS) containing appropriate glucose–electrolyte balance is first-line for mild to moderate dehydration.

• WHO ORS formula: sodium 75 mmol/L, glucose 75 mmol/L.

• For severe dehydration or inability to tolerate oral intake, intravenous fluids (e.g., 0.9% sodium chloride or Ringer’s lactate) should be administered.

2. Diet

• Resume feeding as soon as tolerated; small, frequent meals.

• Avoid high-fat, spicy, or highly sweetened foods during recovery.

• Continue breastfeeding for infants.

3. Antiemetics (for persistent vomiting, especially in children >6 months and adults)

• Ondansetron:

  • Adults: 4–8 mg orally or intravenously every 8 hours as needed.

  • Children (≥6 months): 0.15 mg/kg IV every 8 hours or 0.15–0.2 mg/kg orally as a single dose (max 8 mg).

4. Antidiarrheal agents

• Generally avoided in children.

• In adults without bloody diarrhea or high fever, loperamide may be considered: 4 mg orally initially, then 2 mg after each loose stool (max 16 mg/day).

5. Zinc supplementation (in children in low- and middle-income countries)

• Reduces duration and severity of diarrhea.

• Dose: 10–20 mg daily for 10–14 days depending on age.

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Prevention and Control

Hygiene measures:

• Handwashing with soap and water (alcohol-based sanitizers are less effective against norovirus).

• Disinfect contaminated surfaces with chlorine bleach solution (≥1000 ppm).

• Wash fruits and vegetables thoroughly.

• Cook shellfish to at least 60°C for several minutes.

Isolation:

• Symptomatic individuals should be isolated during illness and for at least 48 hours after symptom resolution.

Outbreak control:

• Temporary closure of affected facilities.

• Enhanced environmental cleaning.

• Exclusion of infected food handlers until 48 hours after recovery.

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Prognosis

• Excellent in healthy individuals; symptoms self-resolve within days.

• Severe illness and death may occur in vulnerable populations, particularly the elderly and immunocompromised.