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Rasko et al. (2011)
performed genetic characterization of the outbreak strain
classifying it within the EAEC pathotype. EAEC of serotype O104:H4 strains
are closely related and form a distinct clade among
E. coli
and EAEC strains.
However, the genome of the German outbreak strain can be distinguished from
those of other O104:H4 strains because it contains a prophage encoding Shiga
toxin 2 and a distinct set of additional virulence (such as AAF/I, Pic, SepA, and
SigA) and antibiotic-resistance genes. Stepwise horizontal genetic exchange
events allowed for the emergence of the highly virulent Shiga-toxin-producing
EAEC strain (
Rasko et al., 2011
). Comparing genomes of related strains iso-
lated during the outbreak suggested that environmental selection enhanced the
magnitude of the outbreak (
Grad et al., 2012
).
Endemic diarrhea in developing countries
EAEC is best known for its role in persistent diarrhea (>14 days) in infants
and children in developing countries. Studies in Mongolia (
Sarantuya
et al., 2004
), India (
Dutta et al., 1999
), Brazil (
Piva et al., 2003
;
Zamboni
et al., 2004
), Nigeria (
Okeke et al., 2000a
,
b
), Israel (
Shazberg et al., 2003
),
Venezuela (
Gonzalez et al., 1997
), Congo (
Jalaluddin et al., 1998
) and many
other countries, have identified EAEC as a highly prevalent (often the most
prevalent)
E. coli
pathotype in infants. The role of EAEC as a cause of per-
sistent diarrhea and malnutrition in Brazil has been demonstrated repeat-
edly (
Lima and Guerrant, 1992
;
Fang et al., 1995
;
Huang et al., 2006
). In
one study, 68% of those with persistent diarrhea shed EAEC in their stools
(
Fang et al., 1995
). In Guinea-Bissau the most common bacteria isolated
from feces of children <2 years of age with diarrhea was EAEC (
Valentier-
Branth et al., 2003
).
Endemic diarrhea in developed countries
A large prospective study in England (
Tompkins et al., 1999
), in which over
3600 cases of diarrhea and controls were studied, found that typical EAEC was
the second most common bacterial cause of gastroenteritis, following
Campy-
lobacter
. EAEC was significantly associated with diarrhea in both prospec-
tive cohorts and in patients presenting to physicians' attention. Typical EAEC
were found as major cause of bacterial diarrhea among infants in Cincinnati,
OH, USA (
Coohen et al., 2005
). A large prospective study of diarrhea was
conducted across all ages in Baltimore, MD, USA and New Haven, CT, USA
and EAEC was significantly associated with diarrhea, being the most common
bacterial cause of diarrhea at both sites (
Nataro et al., 2006
). This observa-
tion has recently been confirmed in a similar study performed in New Jersey
(
Cennimo et al., 2009
). Moreover, a Scandinavian case-control study, found
EAEC in significantly more diarrheal cases than controls (
Bhatnagar et al.,
1993
). This is supported by studies from Germany (
Huppertz et al., 1997
) and
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