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Acute gastroenteritis is defined as diarrheal disease of rapid onset, often with nausea, vomiting, fever, or abdominal pain. It occurs an average of 1.3-2.3 times per year between the ages of 0 and 5 years. Rates among children in child care centers are three times higher. Most episodes of acute gastroenteritis will resolve within 3 to 7 days.

Gastroenteritis in children is caused by viral, bacterial, and parasitic organisms, although the vast majority of cases are viral or bacterial in origin. Twenty five percent of cases may be reported as having "no pathogen," depending on the quality of the laboratory techniques used.

Oral ingestion is the primary route of infection, although rotavirus is transmitted by respiratory or mucous membrane contact.

Viral Gastroenteritis

All of the viruses produce watery diarrhea often accompanied by vomiting and fever, usually not associated with blood or leukocytes in the diarrhea stool or with prominent cramping.

Rotavirus is the predominant viral cause of dehydrating diarrhea. Rotaviral infections tend to produce severe diarrhea, causing up to 70% of episodes in children under 2 years of age who require hospitalization. Rotavirus infection tends to occur in the fall in the southwest of the US, then sweeping progressively eastward, reaching the northeast by late winter and spring.

Norwalk viruses are the major cause of large epidemics of acute nonbacterial gastroenteritis. In schools, camps, nursing homes, cruise ships, and restaurants.

Enteric adenovirus is the third most common organism isolated in infantile diarrhea.

Bacterial Gastroenteritis

The bacterial diarrheas work through the elaboration of toxin (enterotoxigenic pathogens) or through invasion and inflammation of the mucosa (invasive pathogens).

Secretory diarrheas are modulated through an enterotoxin, and the patient does not have systemic symptoms (fever, myalgias) or signs of local irritation of the bowel (tenesmus), or evidence of gut inflammation in the stool (white or red blood cells). The diarrhea is watery, often is large in volume, and often associated with nausea and vomiting.

Invasive diarrhea is caused by bacterial enteropathogens, and is accompanied by systemic signs, such as fever, myalgias, arthralgias, irritability, and loss of appetite. Cramps and abdominal pain are prominent. The diarrhea consists of the frequent passing of small amounts of "mucousy" stool. Stool examination reveals leukocytes, red blood cells, and often gross blood.

The same organisms that typically cause an invasive or inflammatory pattern of illness also may cause a secretory or viral pattern.