Page 162 - AIDSBK23C

Page 162

following ingestion of poorly cooked seafood, should be considered in the differential diagnosis.
Other bacterial pathogens to be considered in cases of colitis include: enteropathogenic E. coli,
Yersinia, and Aeromonas hydrophila.[499,678]
Diarrhea producing (enteropathogenic) strains of E. coli are important worldwide as
causes for diarrhea in travelers and in infants, but also can cause diarrhea in
immunocompromised patients. Such strains can most often be identified by assay specifically
for enteropathogenic E. coli. They may also be known as enteroadherant bacteria.
Histopathologic findings are those of "non-specific" colitis with little crypt distortion or cryptitis,
but with focal epithelial cell necrosis or degeneration, breaks or gaps in the surface epithelium,
aggregates or tufts of epithelial cells, and cellular debris. The inflammatory reaction consists of
a few neutrophils and a moderate increase in lymphocytes. The bacteria are most often seen
along the epithelial surface or brush border and are rarely invasive. Identification methods for
these strains are not commonly available, so empiric antibacterial therapy with response may
suggest E. coli as a cause for AIDS enteropathy.[682]

VIRAL ENTERIC (NON-CMV) INFECTIONS.-- Viruses other than cytomegalovirus
may account for a third of cases of diarrhea in HIV-infected persons, but detection and diagnosis
is more difficult than for the gastrointestinal protozoa. Most involve the small intestine. Viruses
detected have included adenoviruses, rotaviruses, astroviruses, picobirnaviruses, and
caliciviruses. Enzyme immunoassays may detect adenoviruses, rotaviruses, and astroviruses.
Polymerase chain reaction methods with reverse transcription and polyacrylamide gel
electrophoresis can be used to detect picobirnaviruses, which are RNA viruses. Electron
microscopy aids in detection of caliciviruses.[683]
Adenoviruses, similar to the other enteric viruses seen in HIV-infected persons with
weight loss, can account for a chronic, watery, nonbloody, non-mucoid diarrhea. Grossly,
adenoviral lesions may appear discrete, sometimes raised, erythematous lesions several
millimeters in diameter. Adenovirus most often involves the colon, but other areas of the GI
tract may also be affected. Light microscopic features include involvement only of epithelial
cells, and mainly surface goblet cell involvement. The mucosa may demonstrate disorder with
loss of orientation, degeneration, and vacuolization. The inclusions are only located in the
nucleus and appear amphophilic or eosinophilic. The inclusions typically involve the entire
nucleus and may have a crescent or sickle shape, but are rarely targetoid.[684]
Children infected with HIV are more likely to have enterovirus or astrovirus infection of
the gastrointestinal tract, as detected by stool culture, than non-HIV infected children, but they
were no more likely to have rotavirus infection. Rates of virus-associated diarrhea are similar in
the two groups.[685]
Electron microscopic examination helps to confirm light microscopic features of
adenovirus with amphophilic intranuclear inclusions in mucosal cells (usually goblet cells)
surrounded by focal mucosal necrosis and chronic inflammation. Unlike CMV, adenovirus
rarely involves the submucosa.[487,684] Rotavirus infections may produce a watery diarrhea
and are seen more frequently with AIDS outside of the U.S.[487]

MYCOBACTERIOSIS.-- Both Mycobacterium avium-complex (MAC) and
Mycobacterium tuberculosis (MTB) in the GI tract are usually found in the small intestine,
particularly the duodenum, but can also be found in the colon and stomach (Table 5).[423,686]
Mycobacteria can be cultured from stool in about 10% of HIV-infected patients with diarrhea,