Agriculture Reference
In-Depth Information
lamblia (5), and Cryptosporidium parvum (3); an additional 87 outbreaks were docu-
mented without any etiology identifi ed (Sivapalasingam and others 2003). The produce
items implicated most frequently in outbreaks are “salad” lettuce, seed sprout, melon
and cantaloupe (Sivapalasingam and others 2003).
Multiple sprout outbreaks of S. enterica and E. coli O157:H7 illness occurring
worldwide have been associated usually with sprouts (e.g., alfalfa, mung bean, radish)
grown from contaminated seed (Michino and others 1999; Breuer and others 2001;
Mahon and others 1997; Proctor and others 2001; Mohle-Boetani and others 2009).
The seeds are harvested in different parts of the world (e.g., U.S., Australia, China)
under agricultural conditions that in many cases are not controlled well for microbial
safety, considering the eventual ready-to-eat product to be produced. The sprouting
process involves ideal conditions for enriching even a small concentration of pathogen
that may contaminate even a small proportion of the seeds. These conditions empha-
size again the importance of the quality of the preharvest environment to produce
production at every step of the production cycle, including seed and transplant produc-
tion, harvesting, and the fi elds prior to and following harvest (water, fertilizers, crop
debris, human and animal visits). Contaminated seeds are not a major risk factor prob-
ably in the nonsprout outbreaks to be documented further here; however, seeds should
be appreciated as an early preharvest control point in fresh produce production.
Preharvest contamination is suspected in numerous outbreaks associated with leafy
vegetables (lettuce and spinach), tomatoes, cantaloupes, and possibly other commodi-
ties (e.g., jalapeño peppers, April-July, 2008). For U.S.-grown leafy vegetables alone,
there have been more than 20 foodborne outbreaks since 1995 linked to contamination
by E. coli O157:H7, resulting in at least 600 reported illnesses and 5 deaths. Since
2000, at least 12 outbreaks have been linked to Salmonella contaminated tomatoes
(
1600 cases) and 3 outbreaks linked to Salmonella contaminated cantaloupes (72
cases) (Table 1.1). It is worth noting that, during the fi nal preparation of this review,
a major ongoing outbreak of Salmonella in St. Paul is associated with jalapeño peppers
grown in Mexico and distributed by a company in Texas occurred (CDC 2008b). This
was the fi rst reported outbreak associated with this food item; however, additional
details will be required to determine whether the contamination occurred on the farm
or postharvest (packinghouse). Several outbreaks suspected of being associated with
preharvest contamination of tomatoes, lettuce, and carrots by Shigella and Yersinia
species also occurred (Table 1.1). These outbreaks have been listed to emphasize some
emerging produce-pathogen issues of concern: preharvest contamination, pathogen
persistence and/or fi tness in the environment, and diversity of pathogens implicated
depending upon local growing conditions (Table 1.1; e.g., leafy vegetables—Western
U.S./Sweden/Italy, tomatoes — Eastern U.S., cantaloupe — Mexico, Yersinia — Finland).
Previous epidemiological studies of fresh produce outbreaks often lacked defi ni-
tive evidence of the source of contamination and a step within the food production
and processing chain where contamination could have occurred. However, traceback
investigations of E. coli O157:H7-leafy vegetable outbreaks determined that 12 of
them were linked probably to commodity grown on farms in the Salinas Valley,
a region located on the Central Coast of California, and the major supplier of fresh
produce to the U.S. market (Table 1.1; see references for additional details). Indeed,
baby spinach linked to a large multistate outbreak of E. coli O157:H7 in the late
spring of 2006 was grown in a valley adjacent to the Salinas Valley (CalFERT 2007b;
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