++
Diarrhea is an increase in the liquidity and/or frequency
of the stools. It reflects an increase in stool water content due
to impaired water absorption and/or active water secretion
by the intestine. Although the advent of oral rehydration therapy
has dramatically reduced the mortality rates in the past 50 years,
diarrhea remains a major cause of morbidity and mortality in children,
particularly among those in developing countries.1 Most
episodes of diarrhea occur on the basis of 1 of 5 mechanisms: malabsorptive,
secretory, osmotic, dysmotility, and inflammatory. Malabsorption
is due to a decrease in absorptive surface area, as occurs after
intestinal resection (short bowel syndrome) or with intestinal villous
atrophy, as seen in celiac disease. Secretory diarrhea is caused
by secretagogues such as bacterial toxins (eg, cholera), gut regulatory
peptides (eg, vasoactive intestinal polypeptide), short-chain fatty
acids, and bile salts, which can induce intestinal water secretion
while inhibiting absorption. Secretory diarrhea characteristically
persists even when the patient is in a fasting state. Osmotic diarrhea
results from the intraluminal presence of malabsorbed solutes, such
as lactose, which exert significant osmotic pressure that results
in secretion of water into the intestines. Osmotic diarrhea characteristically
decreases or stops completely during fasting. Dysmotility can lead
to increased peristalsis, causing diarrhea due to rapid transit,
or to decreased peristalsis, leading to bacterial overgrowth as
the cause of diarrhea. Inflammatory disorders cause diarrhea by
decreasing the mucosal absorptive capacity and/or through
disturbances in motility. One or more of these mechanisms may be
operative in an individual during an episode of diarrhea.
++
Acute diarrhea accounts for 2 to 3 million deaths per year with
most occurring in young children in developing countries. In the
United States, approximately 220,000 children under 5 years of age
are hospitalized each year for acute diarrheal illnesses, accounting
for 9% of all hospitalizations in this age group.2
+++
Clinical Features
and Differential Diagnosis
++
The common causes of acute diarrhea are listed in Table
385-1. Enteric infections account for most cases of acute diarrhea
in children with diarrhea secondary to nonenteric infections, such
as urinary tract, respiratory, or systemic infections, accounting
for a smaller number of cases.3 Detailed information
regarding each specific pathogen is found in Section
17. Viruses are responsible for the majority (60–80%)
of enteric infections in children, especially those under the age
of 2 years. Of these, rotaviruses are most prevalent and most likely
to cause dehydrating diarrhea. Of all children requiring treatment
for dehydration during the peak winter gastroenteritis season, 70% to
90% have rotavirus infection.4 Other winter-predominant
viral agents, such as astroviruses and caliciviruses, tend to infect
older children and cause illness of shorter duration. Viral gastroenteritis
is typically transmitted by the fecal-oral route, but outbreaks
in a community setting suggest the possibility of airborne spread
as well, perhaps following episodes of vigorous emesis.5 The
norovirus (or Norwalk agent), a calicivirus, is an important cause
of foodborne outbreaks of gastroenteritis ...