VIRAL GASTROENTERITIS

Definition: Gastroenteritis means inflammation of the stomach and small and large intestines. Viral gastroenteritis is an infection caused by a variety of viruses (see table) that results in vomiting or diarrhea (never bacterias or parasites as pathogens). It is often called the "stomach flu," although it is not caused by the influenza viruses.

Infections: The clinician encounters acute viral gastroenteritis in 3 settings:
a) Sporadic gastroenteritis in infants, most frequently is caused by rotavirus.
b) Epidemic gastroenteritis, which occurs either in semiclosed communities or as a result of classic food-borne or water-borne pathogens; mostly caused by Norwalk-like viruses (NLVs).
c) Sporadic acute gastroenteritis of adults, which most likely is caused by Norwalk-like viruses, other caliciviruses, rotaviruses, adenoviruses and astroviruses.

Symptoms: The main symptoms of viral gastroenteritis are watery diarrhea and vomiting. Affected person may also have headache, low fever and abdominal cramps (stomachache). Symptoms begin one to two days following infection and may last for one to 7 days, depending the virus type.

Seriousity of illness: People who get viral gastroenteritis almost recover completely without any long-term problems. Gastroenteritis is a serious illness for persons who are unable to drink enough fluids to replace what they lose through vomiting or diarrhea; infants, young children and persons who are unable to care for themselves (elderly and immune-compromised persons).

Contagiousity and spread: Yes, viral gastroenteritis is contagious; viruses are spread by three main ways (in order of importance):
a) Person-to-person: Close contact with infected persons; Communities, Hospitals, Elderly homes
b) Foodborn: Infected by eating or drinking contaminated foods: Seafood, salads, sandwiches
c) Airborn: Infection by inhalation of contaminated drops: takes more and more importance

Contamination of food:
a) Contamination by food preparers or handlers who have viral gastroenteritis, especially if they do not wash their hands regularly after using the bathroom or changing diapers.
b) Contamination by sewage: Drinking water, vegetables and fruits irrigated on surface and shellfish, especially molluscan shellfish like oysters, may be contaminated by sewage and cause severe outbreaks. As water quality testing (for drinking water and shellfish harvesting areas) is performed using bacterial indicators for faecal contamination, which do not correlate with viral pathogens, virus contamination is not considered and remains a risk.

When (seasonality) does viral gastroenteritis occur? Each virus has its own seasonal activity.
Norwalk-like viruses, which are the main cause of viral gastroenteritis worldwide, seem to have the highest activity in winter.Rotavirus and astrovirus infections also occur incooler months, whereas adenovirus infections occur throughout the year. The reason for the winter seasonality of most gastrointestinal viral infections could be explained by a higher receptivity of human mucosals for viruses during cold seasons, since most people suffer from chronic low-level inflammations during these periods.

Who Gets Viral Gastroenteritis? Viral gastroenteritis occurs in people of all ages and backgrounds. However, some viruses tend to cause diarrheal disease primarily among people in specific age groups. Rotavirus infections is the most common cause of diarrhea in infants and young children under 5 years old. Adenoviruses and astroviruses cause diarrhea mostly in young children, but older children and adults can also be affected. Norwalk-like viruses are the main cause worldwide for diarrhea in older children and adults. The US Centers for Disease Control and Prevention estimate that viruses cause 9.2 million (out of a total of 13.8 million from all causes) cases of food-related illness each year.

Mortality: Rotavirus infantile gastroenteritis is the predominant cause of infant mortality in the developing world. In the United States and probably in most parts of the world, elderly persons have the highest risk for death from gastroenteritis. The role of Caliciviruses (NLVs etc.) becomes evident since their detection became possible in the 90's, since they may kill more people in the United States than do rotavirus disease, as an example.

Dignosis of viral gastroenteritis:
Physician: Generally, viral gastroenteritis is diagnosed by a physician on the basis of the symptoms and medical examination of the patient. The presence and the degree of dehydration can be determind by following criterias: Vitality (usually normal), temperature (slightly elevated; high fever suggests bacterial infection), hypotension (suggest severe dehydration). Other signs of dehydration include poor skin turgor, dry mucous membranes, and extreme fatigue or drowsiness.
Laboratory: If physicians suspect an outbreakof viral contamination, the may verify the presence of viruses using appropiate methodologies to identify the pathogene. Different laboratory methods exist to identify viral pathogens. Diagnosis can be based on Enzyme-linked Immunoassays (EIA) (>98% sensitivity and specificity), latex agglutination tests (less sensitive and specific compared to EIA) and most recently by molecular biological methods like Polymerase-Chain-Reation (PCR). Especially for Norwalk-like viruses, which can not be grown on cell culture and which have a great diversity of surface-antigens, diagnosis by PCR and phlyogenetic analysis in last years rises the importance of these viruses as main cause of viral gastroenteritis.

Treatment of viral gastroenteritis: The most important treatment of viral gastroenteritis in children and adults is to prevent severe loss of fluids (dehydration). This treatment should begin at home and physician may give specific instructions about what kinds of fluid to give. Medications, including antibiotics (which have no effect on viruses), antiemetics and antidiarrheal agents treatments, should be avoided unless specifically recommended by a physician. Shock, severe dehydration, and decreased consciousness require hospitalization and intravenous therapy.

Prevention of viral gastroenteritis: Persons can reduce their chance of getting infected by taking care with infected persons. Frequent hand washing, prompt disinfection of contaminated surfaces with household chlorine bleach-based cleaners and prompt washing of soiled articles of clothing may prevent contamination by person-to-person-contacts and airborn ways. Avoid food or water that is thought to be contaminated.

Vaccination for Viral Gastroenteritis: There is no vaccine or medicine currently available that prevents viral gastroenteritis. A vaccine was approved in 1998 that protects against severe diarrhea from rotavirus infection in infants and young children. Following careful surveillance of large-scale introduction of the first licensed rotavirus vaccine, the producer of that vaccine has now withdrawn it from the market. For the latest news on rotavirus vaccines, please visit The Vaccine Page. For detailed vaccine strategies, please visit The University of Leicester.