In the United States, children younger than 3 years of age have 1.3 to 2.3 episodes of diarrhea each year. The prevalence is higher in children attending day-care centers. Up to one-fifth of all acute-care outpatient visits to hospitals are by families with infants or children affected by acute gastroenteritis, and 9 percent of all hospitalizations of children younger than 5 years of age are for diarrhea. 1 Most enteric infections are self-limited, but excessive loss of water and electrolytes, resulting in clinical dehydration, may occur in 10 percent and is life threatening in 1 percent. 2
Pathogenic viruses, bacteria, or parasites may be isolated from nearly 50 percent of children with diarrhea. Viral infection is the most common cause of acute diarrhea. Bacterial pathogens may be isolated in 1 to 4 percent of cases. While infants and children who attend day-care centers are most likely to acquire viral gastroenteritis, they are at increased risk of acquiring a variety of enteric infections/infestations by Shigella, Campylobacter, Clostridium difficile, Salmonella, Cryptosporidium, and Giardia lamblia. The attack rate during outbreaks may range from 30 to 100 percent, and shigellosis is particularly contagious. 3
Enteric infections causing diarrhea are spread by the fecal-oral route by contaminated food, water, and fomites. Rotaviruses, Norwalk viruses, the enteric adenoviruses, calicivirus, and astroviruses are the most recognized viral pathogens that affect children. Of these, rotavirus is the most common, typically occurring in the cooler months of the year in North America (October to April), and infecting every child in the United States by age 4 years. This virus causes potentially lethal dehydration in 0.75 percent of children younger than 2 years of age. 4 Older children and adults have acquired immunity against the rotaviruses and are less likely to develop the severe dehydrating syndrome. Symptomatic enteric adenovirus (EAd) infection with serotypes 40 and 41 causes diarrhea that is associated with concurrent respiratory symptoms. Infections, with no clear peaks, occur throughout the year and may be responsible for 5 to 20 percent of hospitalizations for childhood diarrhea.5 Outbreaks of EAd infection occur second only to rotavirus infection in prevalence. Norwalk virus infection is also implicated in causing epidemic gastroenteritis. In addition to developing nausea, vomiting, diarrhea, and abdominal cramps, affected children and adults may have headache, fever, chills, and myalgias. Vomiting is more prevalent in children, whereas diarrhea is more common in adults.
The major bacterial enteropathogens in the United States are Campylobacter jejuni, Shigella species, Salmonella species, Yersinia enterocolitica, Clostridium difficile, Aeromonas hydrophila, and Escherichia coli. Escherichia coli is the most common bacterial organism causing diarrhea in children around the world but is less common in the United States. Diarrhea due to E. coli may be watery and caused by enterotoxigenic E. coli (ETEC) or enteropathogenic E. coli (EPEC), or present as a dysentery-like disease due to infection with enterohemorrhagic E. coli (EHEC).
Giardia lamblia is a common cause of diarrhea in infants and young children in day-care centers. As many as 50 percent of infected children may be asymptomatic. Cryptosporidium infestations occur in a similar epidemiologic pattern. Although Cryptosporidium was first recognized as an opportunistic pathogen in immunocompromised children, it is now recognized as a cause of protracted watery diarrhea in otherwise healthy children. Entamoeba histolytica causes diarrhea, proctitis, dysentery, or hematochezia. Symptomatic infection in children results from exposure by travel to a geographic locale endemic for the organism or in adolescents through sexual transmissions.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.