Agriculture Reference
In-Depth Information
Table 1.4.
Incidence of pathogenic
E. coli
and
S. enterica
in municipal and agricultural
watersheds
Description
Pathogen
Reference
Alberta, Canada; watershed near
agriculture; 1999 - 2000; not
associated with manure output
E. coli
O157:H7
(13/1483 = 0.9%)
Salmonella
(88/1429 = 6.2%)
Johnson and others 2003
Baltimore, MD, area, U.S.; 2002-04;
potential pathogens
E. coli
,
tir
and/or
Stx- pos
(653/1218 = 53%)
Higgins and others 2005
California, central coast, U.S.;
agricultural and urban watershed;
2005 - 06
E. coli
O157:H7
(38/584 = 6.5%)
Cooley and others 2007
France, near Mediterranean;
agricultural and urban; 1996-97
Salmonella
(574/? = ?)
a
Baudart and others 2000
Central African Republic; N ' Goila
E. coli
O157:H7
(6/260 = 2.3%)
Tuyet and others 2006
Cornwall, U.K.; freshwater stream
crossing beach; 2004;
outbreak - associated
E. coli
O157:H7
(5/? = ?%)
a
Ihekweazu and others 2006
Georgia, U.S.; single day, 83 sites
on river; 2005
Salmonella
(62/83 = 75%)
Meinersmann and others
2008
a
Total number of samples tested was not noted.
with potential pathogens (Higgins and others 2005). However, the lack of any evidence
of human illness associated with these strains suggests that they are not highly virulent
compared to
E. coli
O157:H7.
Four of the studies listed in Table 1.4 were initiated as a result of high levels of
illness and outbreaks of
E. coli
O157:H7 associated with exposure to water or food
(Johnson and others 2003; Ihekweazu and others 2006; Tuyet and others 2006; Cooley
and others 2007). One of these studies of a watershed in a major leafy vegetable
production region of the U.S. was initiated as a result of three separate outbreaks of
E. coli
O157:H7 linked to leafy vegetables grown in the Salinas Valley region of
California (Table 1.1), and possibly linked to a single farm (Cooley and others 2007).
Water samples obtained monthly on average from
<
20 sites, most within approxi-
mately 30 km of one another, revealed that
6% of the samples were positive for
E.
coli
O157:H7. Sites nearby cattle grazing in elevated regions of the watershed were
positive more frequently, and samples obtained during or subsequent to heavy rain
events with increased water fl ow correlated with increased incidence at specifi c sites.
Also, strains indistinguishable or highly related by genotype were isolated at the same
time up to 30 km apart, or from the same sites months apart (Cooley and others 2007).
Similarly, outbreak investigations of farms and ranches in the central coast region of
California have provided clues to intriguing fate and transport relationships from
assessment of genotypes of strains of
E. coli
O157:H7 isolated from environmental
and wildlife samples obtained at similar times and locations (Cooley and others 2007;
Jay and others 2007). Predominant strains may be persistent in some environments
and transported by the commingling of wildlife and livestock into watersheds and
possibly fi elds where produce is grown. However, the amounts of pathogen, their
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