What is the epidemiology of stomach flu?

Epidemiology of Stomach Flu (Viral Gastroenteritis)

Viral gastroenteritis affects millions of people globally each year, with norovirus being the most common cause, accounting for 84% of outbreaks with a known etiology in the United States. 1

Causative Agents and Their Prevalence

Norovirus

• Most common cause (84% of outbreaks with identified etiology) 2
• Incubation period: 24-48 hours
• Duration: 12-72 hours
• Symptoms: nausea, vomiting, non-bloody diarrhea, abdominal cramps 1
• Affects all age groups, but illness is most commonly reported among school-aged children and older 3
• Antibody levels reach 50% by middle age in developed countries 3

Rotavirus

• Leading cause of severe diarrhea in children globally 3
• Incubation period: 1-3 days
• Duration: 4-7 days
• Vaccination has reduced infections by up to 90% in children 4
• Peak incidence in winter months in temperate climates 3

Other Viral Agents

• Adenovirus: Accounts for 5-20% of hospitalizations for childhood diarrhea in developed countries 3
• Astrovirus: Accounts for 3-5% of hospital admissions for diarrhea in children 3
• Calicivirus: Found in approximately 3% of children hospitalized for diarrhea 3

Seasonal Patterns

• Most viral gastroenteritis outbreaks (53%) occur during winter months (December-February) 2
• Rotavirus shows a distinct winter peak in temperate climates 3
• Adenovirus infections occur throughout the year with no clear seasonal peaks 3

Age Distribution

• Children under 5 years are most vulnerable to severe disease and hospitalization 1
• By age 12, most persons have been infected with calicivirus, with peak acquisition between 3 months and 6 years 3
• Elderly individuals are also at high risk, particularly in institutional settings 1
• Adults typically develop immunity to many viral agents after childhood exposure, though this may wane with age 3

Transmission Patterns

Primary Modes of Transmission

• Person-to-person contact (most common route) 2
• Contaminated food and water 3
• Environmental contamination of surfaces 2
• Aerosol (particularly with vomiting episodes) 3
• Fomites 3

Outbreak Settings

• 70% of outbreaks occur in long-term care facilities 2
• Child care facilities account for:
  • 59% of shigellosis outbreaks
  • 36% of salmonellosis outbreaks
  • 32% of other or multiple etiology outbreaks 2
• Institutional settings (schools, hospitals, nursing homes) are common for calicivirus outbreaks 3

Global Distribution

• Viral gastroenteritis occurs worldwide
• In developing countries, antibodies to viral agents are acquired at an earlier age than in developed nations 3
• Attack rates in outbreaks can range from 50-70% 3
• Major outbreaks can affect tens of thousands of people, as seen in the 2012 Réunion Island outbreak that affected more than 50,000 people 5

Risk Factors

• Crowded living conditions
• Poor hygiene practices
• Institutional settings (nursing homes, day-care centers, schools)
• Compromised immune systems
• Age extremes (very young and elderly)
• Contaminated food or water sources 3, 1

Disease Burden

• Viral gastroenteritis causes an estimated 179 million episodes annually in the United States 2
• From 2009-2013, reported outbreaks in the U.S. resulted in:
  • 356,532 illnesses
  • 5,394 hospitalizations
  • 459 deaths 2

Prevention and Control Considerations

• Strict hand hygiene (washing with soap for at least 10 seconds)
• Prompt cleaning of contaminated surfaces
• Isolation of ill persons for at least 2 days after symptom resolution
• Food handlers should not prepare food for at least 2 days after illness resolution
• Environmental disinfection with appropriate agents 1

Emerging Trends

• Emergence of new rotavirus genotypes like G12P8 poses risk for global spread 5
• Improved reporting systems have increased documentation of outbreaks 2
• Vaccination programs have significantly reduced rotavirus burden in children 4

Understanding the epidemiology of viral gastroenteritis is crucial for implementing effective prevention strategies and reducing the substantial morbidity associated with these infections, particularly among vulnerable populations like young children and the elderly.