Agriculture Reference
In-Depth Information
The use of animal manure (either composted or raw) for animal production was
clearly linked to contamination with generic
E. coli
(Odds ratio = 13). Among
the different types of manure, cattle manure was approximately seven times more
likely to be associated with
E. coli
contamination in produce. The season of manure
application (fall or spring) did not appear to increase
E. coli
prevalence. When
manure was aged for more than 6 months before application, it was four times less
likely to contaminate produce than in farms that used manure aged for less than
6 months.
Researchers at the University of Wisconsin conducted a couple of studies specifi -
cally designed to reevaluate the requirement for 120 days of manure application before
harvest based on generic
E. coli
survival (Ingham and others 2004, 2005). In the fi rst
study, the count of naturally occurring
E. coli
declined 3 log CFU/g within 90 days
in manure-amended soil from an initial count of 4.4 log CFU/g, but it was still detected
after 168 days. Based on the rapid die-off, the researchers indicated that the Organic
Rule could be shortened to less than 120 days. In the second study, there was also
an initial decline of 2.5 log CFU/g in the
E. coli
count during the fi rst 7 weeks,
but the indicator was still detected in radish, lettuce, and carrot samples. The investi-
gators concluded that this data was not suffi cient evidence to reduce the 120-day
requirement.
A couple of recent publications compared the effect of conventional and organic
soil type on the survival of
E. coli
O157:H7 (Franz and others 2008; Semenov and
others 2008). In the fi rst study, there was no signifi cant difference between organic
and conventional soils and the range of maximum survival times ranged from 54 to
105 days. In the second report, soil types were paired by organic and conventional
categories and the decline in pathogenic
E. coli
appears to be very irregular in con-
ventional soils as compared to organic, but there were again no signifi cant differences
in the overall rate of inactivation.
Epidemiology of Foodborne Disease Linked to Organic Produce
In the last 10 years there have been from 1,000 to 1,300 recorded outbreaks of food-
borne disease per year in the U.S., but there is no recorded outbreak in the Centers
for Disease Control Outbreak Surveillance Data that was confi rmed to an organic food
(CDC 2007). However, a few reports have linked some infections to consumption of
organic fresh produce. In Germany, a rare outbreak of gastroenteritis and hemolytic
uremic syndrome were caused by organically grown parsley contaminated with vero-
toxigenic
Citrobacter freundii
(Tschape and others 1995). The parsley had been grown
in an organic garden fertilized with pig manure, but it is not clear whether this garden
had been certifi ed by an organic agency. In a couple of outbreaks of
E. coli
O157:H7
due to contaminated lettuce, the traceback investigations reported that manure had
been used in the fi elds where the lettuce had been grown, but none of them indicated
that the farms were using certifi ed practices (Ackers and others 1998; Hilborn and
others 1999 ).
In one of the most serious outbreaks due to fresh produce, bagged spinach pro-
duced in California was responsible for more than 200 infections with
E. coli
