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| David J. Weber |
Acute
gastroenteritis is one the most common illnesses, affecting both adults and
children. Infection is the most common
cause of acute gastroenteritis.
Pathogens include viruses (e.g., norovirus, rotavirus), bacteria (Campylobacteria, Salmonella, Shigella, E. coli, Clostridium difficile), and
protozoans (e.g., Giardia,
ameba). Among viruses the most causes of
infection are human caliciviruses (including noroviruses and sapoviruses), enteric
adenoviruses, rotaviruses, and astroviruses.
However, the caliciviruses, principally noroviruses, are the most common
cause of acute gastroenteritis in both adults and older children with an
estimated 23 million illnesses in the United States each year.
Noroviruses
contain a single-strained RNA genome. As
with other RNA viruses there is substantial genetic diversity among these
viruses. Noroviruses are subdivided into
five genotypes based on sequence homology.
Genogroups GI, GII and GIV include human pathogens and multiple
genotypes are recognized within each group.
Noroviruses
cause an average of 20 million total illnesses, 1.8 million physician visits,
400,000 ED visits, ~60,000 hospitalizations, and ~700 deaths per year. Young children (i.e., <5 years of age) and
older adults (>65 years of age) are at greatest risk for hospitalization and
death. Although illness occurs
throughout the year, there is a pronounced winter peak (hence the name “winter
vomiting disease”).
Novoviruses
are readily transmitted person-to-person (via the fecal oral route) and spread
through airborne droplets, food, water, fomites, and contaminated
surfaces. As few as 18 viruses are
infectious and viral shedding can occur at levels as high as ~8.0x1010
viruses/gm of stool. Although the major
route of transmission is fecal-oral, there are also observations from outbreaks
that suggest that on occasion airborne transmission can occur, most likely when
virus is aerosolized during vigorous emesis.
Immunity to norovirus is relatively short lived and persons can become
repeatedly infected.
