What causes gastroenteritis?

Causes of Gastroenteritis ("Stomach Bug")

Gastroenteritis is primarily caused by viral pathogens, with norovirus and rotavirus being the most common causes, followed by bacterial pathogens like Salmonella, Shigella, Campylobacter, and parasitic infections. 1

Viral Causes

• Norovirus is the most frequent cause of acute gastroenteritis outbreaks among adults, requiring only 10-100 viral particles for infection, with symptoms typically lasting 12-72 hours 2, 3
• Rotavirus is the leading cause of severe diarrhea among children, accounting for approximately 3.5 million cases annually in the United States, with peak incidence in children 6 months to 2 years of age 1, 2
• Adenoviruses (primarily serotypes 40 and 41) contribute to 5-20% of hospitalizations for childhood diarrhea in developed countries 1
• Astrovirus is another common viral pathogen affecting the gastrointestinal tract, particularly in children 1

Bacterial Causes

• Salmonella is one of the leading bacterial causes of gastroenteritis, exceeding norovirus as a cause of hospitalization and death 1
• Campylobacter accounts for approximately 28% of bacterial gastroenteritis cases in children under 5 years 1
• Shigella accounts for about 21% of bacterial gastroenteritis cases in children under 5 years in the United States 1
• Clostridium difficile is an important cause of antibiotic-associated diarrhea, particularly in healthcare settings 2

Clinical Presentation

• Common symptoms include nausea, vomiting, diarrhea, abdominal pain, fever, headache, myalgia, and malaise 1, 4
• Viral gastroenteritis typically presents with:
  • Incubation period of 24-48 hours 2
  • Acute onset of fever and vomiting, followed by watery diarrhea 2
  • Self-limiting illness lasting 3-7 days 2, 4
• Bacterial gastroenteritis may present with more severe symptoms, including bloody diarrhea and higher fever 5

Transmission Routes

• Fecal-oral route is the primary mode of transmission, through:
  • Person-to-person contact 2, 1
  • Contaminated food and water 1
  • Fomites (contaminated surfaces) 2, 1
• Airborne droplets have been hypothesized as a possible transmission route, especially for norovirus 2, 1

Risk Factors and Epidemiology

• Children under 5 years are at highest risk for severe disease 2, 1
• Immunocompromised individuals may experience prolonged and more severe illness 2, 4
• In the United States, viral gastroenteritis shows seasonal patterns:
  • Rotavirus peaks during winter months (October-April) 2
  • Norovirus is more common during the cold season 2

Diagnostic Approach

• Diagnosis is typically clinical for mild cases that resolve within a week 6
• Laboratory testing is indicated for:
  • Severe or prolonged symptoms 6
  • Bloody diarrhea 6
  • Recent antibiotic exposure (test for C. difficile) 6
• Multiplex PCR testing is preferred over traditional stool cultures 6, 7

Management

• Hydration is the cornerstone of treatment:
  • Oral rehydration for mild to moderate cases 6
  • IV fluids for severe dehydration 6
• Antimicrobial therapy is generally not indicated for viral gastroenteritis 7
• Antibiotics are warranted only for specific bacterial causes:
  • Shigellosis (azithromycin preferred) 7
  • Severe salmonellosis (ceftriaxone or ciprofloxacin) 7
  • Some Campylobacter infections (azithromycin) 7
  • C. difficile infection (metronidazole, vancomycin, or fidaxomicin based on severity) 2

Prevention

• Hand hygiene with soap and water for at least 20 seconds 1
• Proper disinfection of contaminated surfaces with chlorine bleach solution 1
• Exclusion of ill food handlers until 48-72 hours after symptom resolution 1
• Isolation of ill individuals in institutional settings for 24-48 hours after symptom resolution 1
• Rotavirus vaccination has reduced rotavirus infections by up to 90% in children 6

Complications

• Dehydration is the most common complication, especially in young children and elderly 4
• Post-infectious irritable bowel syndrome occurs in approximately 9% of patients 6
• Temporary lactose intolerance may develop following gastroenteritis 6