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reported that EPEC had a worldwide distribution. For decades thereafter, EPEC
was described solely based on the O and H serotypes prevalent amongst chil-
dren under 2 years with diarrhea (
Robins-Browne, 1987
). WHO recognizes
12 EPEC serotypes, including typical and atypical EPEC strains, along with
other diarrheagenic
E. coli
, such as EAEC and EHEC (
Campos et al., 1994
;
Rodrigues et al., 1996
;
Scotland et al., 1996
;
Do Valle et al., 1997
;
Trabulsi
et al., 2002
). However, it is now appreciated that assessments of genotype and
phenotype, and not serotype, are more accurate methods for identifying EPEC.
The use of these descriptors has shed new light on the epidemiological and evo-
lutionary features of this pathogen, in addition to bringing about a change in the
classification of certain strains.
Epidemiology and global impact
EPEC is a major cause of human diarrhea in the developing world; with rare
outbreaks in developed countries typically associated with nurseries and day-
care centers (
Donnenberg and Kaper, 1992
;
Nataro and Kaper, 1998
). Adult
infections are uncommon and typically the result of common source outbreaks
or concordant with other conditions (
Nataro and Kaper, 1998
). Previously, rates
of community-acquired EPEC infection were thought to be highest within the
first 6 months after birth (
Chatkaeomorakot et al., 1987
;
Cravioto et al., 1988
;
Gomes et al., 1991
), but recent studies of children 5 years and younger indicate
that prevalence increases with age (
Behiry et al., 2011
;
Ochoa and Contreras,
2011
). The disparity observed among publications describing age-associated
incidence of infection may be due to changes in EPEC diagnosis, promotion of
breastfeeding, or evolution of the pathogen. Disease severity, however, remains
inversely proportionate to age (
Toledo et al., 1983
;
Cravioto et al., 1990
). In
addition to age, it has been proposed that bacterial load may be a factor in
EPEC-induced diarrhea (
Barletta et al., 2011
). The described incidence of
infection differs greatly among studies, with EPEC-associated diarrhea ranging
from 3-50% (
Gomes et al., 1991
;
Alikhani et al., 2006
;
Nweze, 2010
). Emer-
gent reports, in which EPEC was characterized genetically and not by serotype,
indicate a high prevalence of atypical EPEC (aEPEC), particularly in developed
regions (
Afset et al., 2003
;
Robins-Browne et al., 2004
;
Liebchen et al., 2011
)
and associated prolonged diarrhea with these strains (
Afset et al., 2004
;
Nguyen
et al., 2006
). While humans are the sole reservoir for typical EPEC (tEPEC),
animals may act as reservoirs for aEPEC; this chapter will focus on those typi-
cal and atypical strains affecting humans.
MOLECULAR PATHOGENESIS
Regulation
Over the years, multiple proven and potential virulence factors that help
facilitate EPEC colonization of the intestinal epithelium have been identified.
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