Workers’ personal hygiene, the field’s use prior to planting of produce and the time since the last irrigation are some factors that influence the likelihood of E.coli contamination of spinach on farms prior to harvest, according to researchers.
Weather was also identified as an area where future research was needed to design strategies for control of produce contamination by the Texas and Colorado team.
First author Sangshin Park of Texas A&M University, College Station, said other potential risk factors tested included numbers of workers, farm size, organic vs. conventional production, the use of chemical fertilizers, compost, and manure.
E.coli contamination of spinach on farms in Colorado and Texas was 172 times more likely if the produce field was within 10 miles of a poultry farm, and 64 times more likely if irrigated by pond water, he said.
A repeated cross-sectional study was conducted by visiting spinach farms up to four times per growing season over a period of two years (2010 to 2011).
The researchers assayed 955 spinach samples from 12 farms in the two states, finding that generic E.coli was present on 63 of them (6.6%).
The availability of portable toilets, hand-washing stations for workers in the fields and the absence of grazing or hay production on the fields prior to planting spinach, reduced the risk seven-fold.
Produce contamination was also significantly reduced if the field was not used for hay production or for grazing prior to spinach planting.
In the analysis restricted to organic farms only, the spinach from certified organic farms was less likely to be contaminated with generic E.coli than spinach from noncertified organic farms (OR 0.05).
The low risk of spinach contamination with generic E.coli in the certified farm environment might be attributed to the strict implementation of national organic regulations, said Park et al.
The researchers tested their statistical model for spinach contamination to determine how accurately it was able to pinpoint the level of contamination.
“The assessment of the predictive performance of a developed statistical model is largely omitted from food safety studies,” he said.
The methodology may serve as a useful template for future investigations of contamination on farms.
“Because produce is commonly consumed raw, it would be best to prevent pre-harvest contamination by foodborne pathogens all together or at least to reduce it,” said Park.
Source: Applied and Environmental Microbiology
Online ahead of print, DOI: 10.1128/AEM.00474-13
“Generic Escherichia coli Contamination of Spinach at the Preharvest Stage: Effects of Farm Management and Environmental Factors”
Authors: Sangshin Park, Sarah Navratil, Ashley Gregory, Arin Bauer, Indumathi Srinath, Mikyoung Jun, Barbara Szonyi, Kendra Nightingale, Juan Anciso and Renata Ivanek