GASTROINTESTINAL DISORDERS - Medicine for Mountaineering and Other Wilderness Activities - page 250

Invasive and Noninvasive Diarrhea
In situations where microbiology laboratories that can identify the causative organisms
are not available, distinguishing between noninvasive and invasive diarrhea allows appro-
priate therapy to be administered. Noninvasive diarrhea is caused by organisms that do
not invade the lining of the intestinal tract (the mucosa) but remain in the intestinal lumen
and release toxins that are absorbed and produce diarrhea. (Viruses invade the cells lining
the intestinal tract, but produce a noninvasive type of diarrhea.) Most traveler's diarrhea is
noninvasive. The diarrhea produced by these organisms is less severe than that caused by
invasive organisms, although an exception is cholera, which can be lethal and is a nonin-
vasive infection that causes massive fluid secretion from the gastrointestinal tract.
In contrast, in invasive diarrhea organisms actually penetrate the intestinal mucosa and
can spread systemically throughout the body. Typhoid fever, a form of invasive diarrhea,
typically involves all body tissues. Invasive bacterial infections often are associated with
chills and fever, and with pus, mucus, or blood in the stool, and should be treated with an-
timicrobial agents. Antidiarrheal agents are not recommended because they may aggravate
and prolong the illness.
With the exception of cholera, antimicrobial agents should not be administered for non-
invasive diarrhea. They usually are ineffective and, even when they are helpful, can lead
tothe emergence ofantibiotic-resistant strains oforganisms. However,antidiarrheal agents
may be helpful for these disorders.
Traveler's Diarrhea
Most acute gastroenteritis occurring in visitors to other countries, particularly develop-
ing areas, is noninvasive traveler's diarrhea. About one-third of visitors from the United
States, Canada, and Europe develop diarrhea during travel in such countries. Residents of
developing countries coming to the United States or Europe sometimes develop the same
disorder, which has many colorful names: the Aztec two-step, Delhi belly, Montezuma's
revenge, or simply turista . Such infections are not limited to travelers and involve the nat-
ive population as well.
Enteropathogenic Escherichia coli ( E. coli ), organisms that secrete a toxin that causes
noninvasive diarrhea, are the most common cause of traveler's diarrhea. These bacteria
are normally found in everyone's large bowel, and individuals develop resistance to toxins
from the strains found in their environment. However, exposure to strains to which the in-
dividual has not developed resistance often produces illness.
Other noninvasive bacteria also cause traveler's diarrhea. A high percentage of the
severe diarrheal disorders acquired in the wilderness and in developing countries are of
viral origin. The high incidence of parasitic infestations such as cryptosporidiosis was
not appreciated until the 1980s. Giardia have occasionally been associated with traveler's
diarrhea.