Viruses are the leading cause of acute gastroenteritis in the United States and globally, accounting for the majority of diagnosed acute episodes of community-acquired diarrhea. Acute diarrhea is defined as the sudden passage of loose stools (more than three times per day or at least 200 gm of stool per day) which may be associated with nausea, vomiting, fever, or abdominal pain and a duration of fewer than 2 weeks.
The commonest human pathogens studied are Rotavirus, Caliciviridae (Norovirus and Sapovirus), enteric adenovirus, and Astrovirus. Some Picornaviridae (e.g., Aichivirus) likely cause gastroenteritis while other viral causes of diarrhea remain unproven.
Rotavirus accounted for about 30% to 70% of all hospital admissions in children with acute gastroenteritis prior to the development of a vaccine. This disease tends to peak during winter and in the cooler months. While norovirus is said to be the commonest cause of community-acquired diarrhea, gastroenteritis outbreaks, and foodborne disease in the United States and globally. Noroviruses are efficiently spread from person-to-person. The recent estimate in the United States for the incidence of norovirus infection accounts for up to 800 deaths, 71,000 hospitalizations, 400,000 emergency department visits, 1.9 million outpatient visits, and 21 million morbidities annually.
The adenoviruses are generally less infectious than rotavirus or norovirus with an overall lower medical impact. Two known fastidious strains serotypes 40 and 41, have been shown to be responsible for gastroenteritis in children less than two years old and in daycare.
In severe forms of rotavirus infection, duodenal biopsy specimens obtained from young children have demonstrated denuded villi and flattening epithelial surfaces, leading to villus blunting and malabsorption. The NSP4, which is an enterotoxin released by rotavirus stimulates intestinal secretion, causing diarrhea.
The norovirus viruses are highly contagious with a median infectious inoculum of 18 to 1000 viral particles.it can be transmitted via person-to-person, food, water, airborne and fomite. The viruses exhibit error-prone replication, five genogroups, 30 or more genotypes and thus making humans highly susceptible to repeated norovirus infections for a lifetime.
Enteric adenovirus infection has a long incubation period of 8 to 10 days, but the illness can be prolonged for up to 2 weeks. Enteric adenoviruses are generally less infectious than rota or noroviruses.
Patient with viral etiology of acute gastroenteritis often presents with an intermediate incubation period of about 24 to 60 hours, a short infection duration of 12 to 60 hours, and a high frequency of vomiting. The duration of diarrhea may differ among various viral pathogens. In rotavirus infection, vomiting often heralds the illness, followed by acute watery diarrhea and fever occurring in 1/3 of the population. The illness usually lasts for 5-7 days. Conversely, symptomatic norovirus infections lead to nausea, vomiting, and diarrhea, with a small subset exhibiting only vomiting in children or diarrhea in older adults. The Incubation period occurs from 12 to 48 hours and the resulting illnesses typically last for 1 to 3 days. Lastly, enteric adenovirus infection has a long incubation period of 8 to 10 days, but the illness can be prolonged for up to 2 weeks.
Rapid diagnostic tests are available for the detection of rotavirus antigen and adenoviruses in feces using EIA, latex agglutination, or NAATs. Conversely, noroviruses have been hampered by viral diversity, and thus, norovirus epidemics have traditionally been identified using Kaplan’s criteria. These criteria are comprised of a short incubation period of 1 to 2 days, short duration of illness of 12 to 60 hours and more than 50% of affected persons presenting with vomiting and a negative stool culture. The criteria have a 98% sensitivity of 98% and specificity of 68%. To date, there has been no universal assay that has been approved by the FDA for norovirus infection.
Fluid and electrolyte disorder are the main pathophysiologies of viral gastroenteritis. Sports drinks and broths can support adults who present with acute viral gastroenteritis without signs of volume depletion and have sufficient volume. Adults presenting with mild to moderate volume depletion should be treated with oral rehydration solutions. These are preferred to sports drinks in maintaining electrolyte balance along with hydration. For patients with severe hypovolemia or an inability to tolerate oral rehydration, repletion with intravenous fluids such as normal saline or Ringer’s lactate is required along with oral nutritional supplements, as long as the patient can tolerate them orally. Patients should be encouraged to eat as tolerated with no adherence to any restricted diet.
In general, antimotility and antisecretory drugs appear safe to use in norovirus infections. Viral diarrhea is an acute and self-limited disease that does not require pharmacologic therapy. Infection can be managed outpatient, but indications for hospitalization include severe dehydration, intractable vomiting, renal dysfunction, bloody diarrhea, age older than 65 years, immunocompromised state and pregnancy.
Only two rotavirus vaccines are commercially available, RotaTeq (pentavalent rotavirus vaccine) and Rotarix is monovalent (RV1) vaccine. These vaccines are first administered at two months of age in multiple doses (RotaTeq, three doses at two, four, and six months of age; Rotarix, two doses at two and four months of age).
The differential diagnosis of acute viral gastroenteritis includes other infectious and noninfectious causes of acute diarrhea. An important component in the history obtained from the patient such as hiking, recent travel, oral sexual activities, should prompt evaluation for protozoa such as cryptosporidium and giardia. Recent hospitalization or antibiotics used in the setting of diarrhea should prompt evaluation of Clostridium difficile. Foodborne illness caused by bacterial infections should be suspected when symptoms occur abruptly with shorter incubation period not seen in viral etiology.
Acute viral gastroenteritis is usually temporary and self-limited with a good prognosis. Persons with multiple medical comorbidities are vulnerable and at a higher risk for complications and poorer outcomes. These include:
Prevention occurs both at the individual and community level. Diligent hand hygiene with soap-and-water for 20 seconds is recommended in infected individuals, to help prevent the spread of infection to their family members and colleagues, because of some of the viruses, e.g., norovirus is relatively resistant to alcohol-based hand sanitizers. For disease outbreaks, especially in the cases of norovirus infection occurring in health care and long-term care facilities, standard enteric precaution measures involves careful handwashing, and the use of barriers, such as wearing gloves is advocated. Environmental cleaning with the removal of visible material, followed by 1000 ppm to 5000 ppm chlorine bleach solution cleaning is also recommended. Generally, sick individuals are advised to be excluded from work for 48 to 72 hours post-illness. In cases of an outbreak of contamination of an identified water or food source, public health measures should be directed at the identified sources.