Viral Gastroenteritis
also see Diarrhea, Diarrhea of Infancy, Chronic nonspecific (Toddler's diarrhea)

Diarrhea is probably the leading cause of childhood mortality in the world, 5-10 million deaths per year. In early childhood, the most important cause is rotavirus. Also lead to significant mortality secondary to malnutrition.

Labs. In viral AGE, Isotonic dehydration with acidosis, stools  free of blood and WBC, serum WBC may be elevated but no marked left shift as seen in invasive bacterial enteritis.  Keep in mind: Normally, the intestines preferentially secrete potassium bicarbonate into the lumen and reabsorb sodium chloride. Because diarrheal stools are high in in potassium, increased stool output can lead to depletion of potassium stores.

Ddx: bacterial, protzoan, and occasional surgical (appy, SBO, intussuseption) may mimic viral AGE. Question the dx of viral gastroenteritis if persistent high temp, blood or WBC in stool, or persistent severe or bilious vomiting.

Rx: Avoid and Tx dehydration.Maintain nutritional status.  No benefit of antiemetics, antidiarrheals (controlled studies). No abx. Experimental tx of Ig with severe gastroenteritis.

Px:  After initial natural infxn, limited protection against subsequent infxn and diarrhea (38%, 77%), but good protection against severe diarrhea (87%)

Prevention: hygeine, handwashing, breast feeding -  variable protection observed in a number of studies.
 
Supportive Rx:  

• Rehydrate PO with appropriate Na/Glucose soln to promote optimal fluid absorption.
• see Oral Rehydration Therapy
• No particular carbs (ie rice) or aa improves efficacy of these solutions in viral GE.
• Clears (flat soda, fruit juice, sport ,drinks) are inappropriate for rehydration in kids with sig stool loss.
• Rehydrate PO/NG over 6-8 h, then feed immediately; continue as supplement. Initial IVF if in shock or intractable vomiting.
• After rehydration, resume reg diet for age; results in more rapid recovery from AGE.  >12 h of exclusive clear liquids or dilute formula is without clinical benefit.
• Continue breast feeding even during rehydration.
• Can use lactose-free feedings (soy or lactose free cow's milk) for several days, although not necessary for most children
• hypocaloric diets low in protein/fat not superior to reg diet (i.e. BRAT - banana, rice, applesauce, toast).
• (vs opinion from E-medicine.com, "Foods containing complex carbohydrates (eg, rice, wheat, potatoes, bread, cereals), lean meats, fruits, and vegetables are encouraged. Fatty foods and simple carbohydrates should be avoided" (Dehydration 9/04 http://www.emedicine.com/PED/topic556.htm))

Viral pathogens of diarrhea include

• Rotavirus, the most important cause of severe dehydrating diarrhea in the world   
• Astroviruses, the 2nd most important agent in young children.
• Norwalk agent, very common, a calicivirus, named after locations of initial outbreaks (Snow Mountain, Montgomery county, Sapporo)
• Enteric Adenovirus (Serotypes 40,41). Many serotypes, often acusing URI, but 40 and 41 don't cause resp sx.

Rotavirus

Who: In children under 5 (most severe in 3 m/o to 2 y/o). Serologic evidence of infection Serologic evidence of infection seen in virtually all children by age 4-5. If < 3 mo, protected by transplacental Ab & possibly breastfeeding. Infections in neonates and adults virtually asymptomatic. Immunocompromised pts may experience renal and hepatic involvement. Pts with short bowel syndrome are likely to acquire severe rotavirus infxn.

What: 70 nm, double stranded, segmented RNA virus

When: Winter months

Where: worldwide. Peak spreads from west to east (Nov to May). In california, peak in Feb. Outbreaks common in children's hospitals, day care centers

Why: Infects, destroys mature villous tip cells of SI (brush border, responsible for disaccharide hydrolysis and water/electrolyte absorption via glucose and aa cotransporters), not intestinal crypt cells or colonic epithelial cells, nor gastric mucosa; we are left with functionally immature crypt cells without brush border, and abnormalities in electrolyte and carbohydrate absorption (ie. complex carbs like lactose) ensue. Shed in stool at very high concentrations before, and for days after clinical illness

How: 2-3 day incubation period, predictable sequence of mild/mod fever (abates on day2) vomiting ->diarrhea -> frequent, watery, (no gross blood, no white cells) which lasts 5-7 days

Dx by stool ELISA. Usually can dx based on clinical and epidemiologic features.

Tx: supportive, oral rehydration usually successful. Lactose intolerance seen in 1/2 of infants suffering rotavirus infxn, and may last several weeks. Early refeeding after rehydration recommended.

Vaccine: Live attenuated virus derived from 4 strains. Mild fever generally lasting <24 h after doses 1 and 2 in some children. Use suspendended in 1999 - NOT recommended due to increased risk of intussuception, usually after 1st dose, during 1st week.
 

Astrovirus

Like rota, but milder and less significant dehydration

Norwalk agent

• 27 nm virus, the prototype of a large group of viruses associated with AGE outbreaks
• older children > infants
• short 12 h incubation, then vomiting and/or diarrhea, short duration 1-3 days, vomiting and nausea predominate
  clinical and epidemiologic picture looks like food poisoning from pre-formed toxin, i.e S. aureus, B. cereus.
• Tx: supportive, similar to rotaviral tx

Enteric Adenovirus (serotypes 40,41)

• young children
• like rotavirus, but diarhhea may last longer, often 10-14 days
• year round.

Source: Nelson's, NMS Pediatrics