Agriculture Reference
In-Depth Information
Outbreaks associated with these commodities occurring since 2000 have led to propos-
als and active studies to identify the risk factors that may enhance preharvest contami-
nation of produce. However, no single risk factor can explain these multiple outbreaks
associated with different production environments, processes, produce items, and
pathogens. Rather, it is probable that a convergence of multiple dynamic events
involving more than one factor are required to cause major, noticeable outbreaks. Each
outbreak may be caused by one or more events different from other outbreaks, even
though some common factors are suspected, such as the probable source (e.g., live-
stock, wild animal) and mechanisms of transport from a source to a fi eld (e.g., water-
sheds, animal intrusions, aerosols). However, the mechanisms of survival of pathogens
in complex environments, and locations and conditions where amplifi cation of their
numbers might occur, have not been well documented.
Reviews describing the sources, fate, and transport of pathogens as potential risk
factors relevant to preharvest contamination have been published previously; they
provide background and specifi c details that will be summarized in this review.
Studies of the incidence and fi tness of
E. coli
O157:H7 and
Salmonella
in the produce
production environment associated with leafy vegetables, tomatoes, and cantaloupes
will be emphasized since they have been associated with multiple outbreaks suspected
of being caused by preharvest contamination in the U.S. and Mexico. However, the
same environmental factors described for these two pathogens and implicated com-
modities will apply generally to other pathogens associated with produce contamina-
tion, except for specifi c fi tness characteristics that might be linked to a specifi c
commodity. Information related to the incidence and survival of bacterial pathogens
and fecal indicators in the production environment, and potential transport processes
and risk factors associated with growing fresh produce in dynamic, agricultural
regions are presented.
Outbreaks Associated with Selected Fresh Produce Commodities
An unintended consequence of the increased production and consumption of fresh
produce is an increase in the number of outbreaks of foodborne illness (CSPI 2007;
Sewell and Farber 2001; Sivapalasingam and others 2004). The produce items and
types of pathogens associated most frequently with outbreaks in the U.S. (Sivapalasingam
and others 2003) and other industrialized countries (Sewell and Farber 2001) have
been reported previously, and documented in previous review articles about this
subject (Nguyen and Carlin 1994; Beuchat 1996, 2006; Seymour and Appleton 2001;
Harris and others 2003; Mandrell and Brandl 2004; Johnston and others 2006b).
However, selected data related to outbreaks linked with fresh leafy vegetables and
tomatoes will be emphasized in this review in support of the theory that multiple recent
outbreaks have resulted from preharvest contamination, especially large multistate
or multicountry outbreaks (Table 1.1 ).
The total number of cases of foodborne illness in the United States has been esti-
mated to be approximately 76 million illnesses per year, associated with 325,000
hospitalizations and 5000 deaths (Mead and others 1999). In a recent review of out-
breaks associated specifi cally with fresh produce, the U.S. Centers for Disease Control
and Prevention (CDC) analyzing data from the CDC Foodborne Outbreak Surveillance
