Biology Reference
In-Depth Information
et al., 2001 ). Consequently, low doses of bacteria present in food products are
sufficient to elicit serious infections. Contamination of meat with feces or intesti-
nal contents of cattle during slaughter followed by consumption of undercooked
meat is considered the most common route of transmission. Hamburger pat-
ties made from ground beef have caused a strikingly large number of outbreaks
in the US ( Rangel et al., 2005 ). Specifically, between 1982 and 2002, 41% of
all food-borne E. coli O157:H7 outbreaks were associated with contaminated
ground beef. Other common food vehicles of STEC include unpasteurized milk
and other dairy products, fruit juices, and leafy vegetables. The significance of
vegetables as a source of STEC infection has been increasing in the recent past
as several outbreaks in the US and Europe were mediated by vegetables such as
spinach, lettuce, alfalfa, and bean sprouts ( Table 5.4 ) ( Centers for Disease Control
and Prevention, 2012 ). Contamination of irrigation water with animal feces is
believed to be the source of tainted vegetables in such outbreaks. Interestingly,
E. coli O157:H7 utilize multiple mechanisms to colonize and persist in plants,
e.g. survival in the substomatal cavity and intercellular spaces of leafy greens
( Itoh et al., 1998 ; Solomon et al., 2002 ), in some cases utilizing the T3SS ( Shaw
et al., 2008 ; Xicohtencatl-Cortes et al., 2009b ). Finally, certain unconventional
food vehicles have also been identified in recent multistate STEC outbreaks in the
US including prepackaged raw cookie dough (2009), Lebanon bologna (2011),
and in-shell hazel nuts (2011) ( Centers for Disease Control and Prevention, 2012 ).
Animal contact, contaminated water, and environment are other impor-
tant agents of transmission. In the 90 outbreaks that occurred between 1982
and 2006 in the US, Canada, UK, Ireland, Denmark, Norway, Finland,
and Japan, 7.8% were transmitted by animal contact, 6.7% by water, and
2.2% by other environmental sources ( Snedeker et al., 2009 ). Transmis-
sion from the environment is strikingly predominant in Scotland where
54% of outbreaks between 1994 and 2003 were environmental ( Strachan
et al., 2006 ). Occupational infections have also been reported in labora-
tory personnel ( Spina et al., 2005 ). Additionally, it has been estimated that
approximately 20% of the cases within an outbreak are caused by secondary
person-to-person transmissions, and perhaps a greater proportion during
outbreaks in day care and institutional facilities ( Parry and Salmon, 1998 ;
Snedeker et al., 2009 ).
Clinical features and complications
STEC disease displays a spectrum of manifestations varying from asymp-
tomatic carriage to diarrhea to lethal HUS. The average incubation period for
STEC infection is 3.7 days ( Bell et al., 1994 ). The disease starts as non-bloody
diarrhea, which lasts for 1-3 days followed in 90% of the cases by bloody
diarrhea due to severe hemorrhagic colitis. Most patients remain afebrile and
the abdominal pain is more severe compared to other bacterial gastroenteri-
tis ( Tarr et al., 2005 ). Abdominal tenderness and painful defecation are also
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