What is the etiology of gastroenteritis in individuals of all ages, particularly in children, older adults, and immunocompromised individuals?

Etiology of Gastroenteritis

Gastroenteritis is caused predominantly by viral pathogens across all age groups, with bacteria and parasites accounting for a minority of cases, though bacterial etiologies cause disproportionately more severe disease requiring hospitalization.

Viral Etiologies

Children

• Rotavirus was historically the leading cause of severe gastroenteritis in children <5 years before vaccine introduction, causing an estimated 3 million annual episodes, >500,000 outpatient visits, 27,000 hospitalizations, and approximately 25 deaths in the United States 1
• Norovirus has now assumed the lead as the most common pathogen in children since rotavirus vaccine introduction, associated with nearly 1 million ambulatory care visits and 14,000 hospitalizations annually 1
• Enteric adenoviruses (types 40 and 41) cause endemic diarrhea in young children worldwide 2
• Astroviruses contribute to endemic childhood diarrhea and are found more frequently in pediatric wards and day-care facilities 1
• Caliciviruses affect children in institutional settings and can cause both endemic and epidemic disease 1, 2

Adults

• Norovirus (Norwalk-like viruses) is the predominant cause of epidemic viral gastroenteritis in adults, accounting for 58% of all gastroenteritis illnesses 1
• Norovirus affects travelers returning from developing countries, parents caring for infected children, immunocompromised persons, and older adults 1
• Rotavirus can cause gastroenteritis in adults, particularly in healthcare workers and caregivers exposed to infected children 1

Transmission Characteristics

Viruses are transmitted primarily by the fecal-oral route through close person-to-person contact and fomites, with probable transmission through fecally contaminated food and water, and respiratory droplets 1

Bacterial Etiologies

Most Common Bacterial Pathogens in Children <5 Years

The five most common bacterial pathogens cause an estimated 291,000 illnesses, 103,000 physician visits, 7,800 hospitalizations, and 64 deaths yearly 1:

• Salmonella enterica subspecies (42% of bacterial cases) - accounts for 35% of hospitalizations and 28% of deaths from gastroenteritis despite causing only 11% of overall illness 1
• Campylobacter (28% of bacterial cases) - detected most frequently in hospitalized adults with community-acquired gastroenteritis at 35%, though culture-based methods may miss substantial infections requiring serological testing 3
• Shigella (21% of bacterial cases) - causes dysentery with bloody diarrhea 1
• Yersinia (5% of bacterial cases) 1
• E. coli O157 (3% of bacterial cases) 1

Additional Bacterial Pathogens

• Clostridium difficile has been associated with post-infection IBS in up to 25% of cases 1
• Vibrio cholerae has been associated with post-infection IBS development in 16.5% of cases 1

Key Clinical Distinction

Bacterial gastroenteritis causes greater mucosal damage and inflammation compared to viral agents, explaining why bacterial infections account for a higher proportion of severe episodes requiring hospitalization despite viral infections being more common overall 1

Parasitic Etiologies

• Giardia causes gastroenteritis with a relative risk of 3.9 for developing post-infection functional dyspepsia (26% in exposed vs 7% in unexposed individuals) 1
• Entamoeba histolytica can cause gastroenteritis, particularly in returning travelers 3

Age-Specific Patterns

Infants and Young Children

• Viral pathogens (rotavirus, norovirus, adenovirus, astrovirus) dominate, affecting all children worldwide in the first few years of life regardless of hygiene, water quality, food, sanitation, or behavior 2
• Four of five children in the United States will have rotavirus gastroenteritis in the first 5 years of life (pre-vaccine era) 1
• Among children <5 years, 17% of rotavirus hospitalizations occur during the first 6 months of life, 40% by age 1 year, and 75% by age 2 years 1

Older Adults

• Norovirus and caliciviruses are most common 1
• Viruses usually associated with childhood diarrhea (calicivirus, astrovirus) can affect elderly patients, suggesting waning immunity as a predisposing factor 1
• Rotavirus causes gastroenteritis primarily in older adults as one of several high-risk groups 1

Immunocompromised Populations

HIV/AIDS Patients

• Adenovirus and rotavirus are detected more frequently in HIV-positive patients with varying degrees of immunocompromise 1
• Chronic diarrheal excretion of rotavirus, adenovirus, calicivirus, astrovirus, and other viruses occurs in children with AIDS who may never acquire immunity 1

Other Immunodeficiencies

• Patients with congenital immunodeficiency, severe combined immunodeficiency syndrome (SCIDS), hematopoietic transplantation, or solid organ transplantation experience severe, prolonged, and even fatal rotavirus and adenoviral gastroenteritis 1
• Bone marrow transplant recipients with rotaviral and adenoviral infections have markedly increased mortality 1
• Unique manifestations include viremia (antigen detected in serum) and unique genomic rearrangements in patients with T-cell deficiencies 1

Co-Infections

More than one pathogen was found in 22% of hospitalized adults with gastroenteritis, with simultaneous infection significantly more likely in patients with rotavirus (RR 3.6; 95% CI: 1.8-7.4) and Salmonella infections (RR 2.5; 95% CI: 1.2-5.5) 3. Viral-bacterial co-infections in adults are probably underrecognized 3.

Epidemiologic Patterns

Endemic Disease

Viral diarrhea in children caused by group A rotaviruses, enteric adenoviruses, astroviruses, and caliciviruses affects all children worldwide with infections providing immunity from severe disease upon reinfection (except perhaps caliciviruses) 2

Epidemic Disease

Epidemic viral diarrhea is caused primarily by Norwalk-like viruses (norovirus), affecting people of all ages, often transmitted by fecally contaminated food or water, and subject to control by public health measures 2. The tremendous antigenic diversity of caliciviruses and short-lived immunity permit repeated episodes throughout life 2.

Seasonal Variation

In the United States, rotaviruses cause winter seasonal peaks, with activity usually beginning in the southwest during November-December and spreading to the Northeast by April-May 1

Common Pitfalls

• Underestimating viral etiology: Viruses cause approximately 70% of episodes of acute gastroenteritis in children, yet viral infections are often underrecognized compared to bacterial causes 4
• Missing Campylobacter infections: Culture-based methods may miss a substantial proportion of Campylobacter infections; additional serological testing should be considered, as 46% of Campylobacter diagnoses in one study were made solely by serology 3
• Overlooking co-infections: Viral-bacterial co-infections occur in 22% of hospitalized adults but are probably underrecognized 3
• Assuming bacterial etiology in severe cases: While bacterial gastroenteritis causes more severe disease, viral infections (particularly norovirus and rotavirus) remain important causes of severe gastroenteritis requiring hospitalization in both children and adults 1, 3