Hybrid and potentially pathogenic Escherichia coli strains - Escherichia coli: Pathotypes and Principles of Pathogenesis - page 338

in this large outbreak of the HUS associated with E. coli O104:H4 ( Buchholz
et al., 2011 ). Because domestic ruminants, especially cattle, have been identi-
fied as natural reservoirs of Shiga-toxin-producing E. coli , a recent study inves-
tigated whether cattle could be a reservoir of E. coli O104:H4 and a potential
source of transmission to humans ( Auvray et al., 2012 ). A PCR approach target-
ing stx2 , wzx O104 , fliC H4 and aggR genetic markers was used to evaluate cattle
fecal carriage of the outbreak strain; however, the analysis was unable to detect
this pathogen, suggesting that cattle is not a reservoir of the recently emerged
E. coli O104:H4 pathotype ( Auvray et al., 2012 ).
Clinical features
The clinical manifestations during the 2011 European outbreak were divided into
a three-phase disease ( German EHEC-HUS Registry, 2011 ). Most of the patients
suffered from bloody diarrhea and a smaller portion presented with watery diar-
rhea. Some patients did not have stool abnormalities but presented with clinical
or laboratory signs of thrombotic microangiopathy (TMA). Remarkably, the signs
of TMA evolved over a period of 3-5 days in about a third of patients. Mean-
while, the majority of patients completely recovered from the infection. After an
additional 3-10 days, almost 50% of the HUS patients needed dialysis and neu-
rological symptoms developed in a majority of patients with TMA. Intriguingly,
the neurological symptoms ranged from mild disorientation, qualitative and quan-
titative alterations of consciousness, double vision, dysphasia, hyperreflexia and
apraxia to loss of reflexes or repeated epileptic seizures requiring intubation and
mechanical ventilation ( German EHEC-HUS Registry, 2011 ). Such neurological
involvement had only been described in a less severe form of diarrhea-associated
HUS and in very few patients ( Nathanson et al., 2010 ).
Complications
The O104:H4 outbreak was characterized by a higher HUS incidence (25%)
compared with other STEC outbreaks ( Borgatta et al., 2012 ). While HUS is
usually seen in children under 5 years of age suffering, i.e. of STEC O157:H7
infection (for further details, see Chapter 5), the E. coli O104:H4 outbreak
affected mostly individuals above 20 years of age (87%). Also, there was a
predominance of women in both E. coli O104:H4 infections (59%) and HUS
(68%). As indicated above, about one-third of patients developed severe neuro-
logical complications and needed management in intensive care units. Patients
with these neurological complications did not respond to therapeutic plasma
exchange or eculizumab (see below) and because the complications arose 1
week after the onset of diarrhea, the use of an IgG immunoadsorption therapy
was tested in a small number of patients ( Greinacher et al., 2011 ). Although the
study was not controlled, this rescue therapy appeared to show that IgG immu-
nodepletion can improve neurological complications in patients with E. coli
O104:H4-associated HUS and suggested that antibodies might be involved in