Risk Factors Associated with Salmonella and Listeria monocytogenes Contamination of Produce Fields

Strawn, Laura K.; Gröhn, Yrjö T.; Warchocki, Steven; Worobo, Randy W.; Bihn, Elizabeth A.; Wiedmann, Martin

doi:10.1128/aem.02831-13

Cited by 150 publications

(141 citation statements)

References 61 publications

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“…2). Previous work also has shown that generic E. coli (18), E. coli O157:H7 (27), Salmonella (28), and Listeria (29,30) are positively associated with livestock density or proximity to livestock. Similarly, studies that have aggregated reported EHEC illnesses to county or district levels have generally observed higher EHEC infection rates in counties with higher cattle densities, although this approach infers rather than directly links cases and exposures (19,20).…”

Section: Discussionmentioning

confidence: 97%

Comanaging fresh produce for nature conservation and food safety

Karp

Gennet

Kilonzo

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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In 2006, a deadly Escherichia coli O157:H7 outbreak in bagged spinach was traced to California's Central Coast region, where >70% of the salad vegetables sold in the United States are produced. Although no definitive cause for the outbreak could be determined, wildlife was implicated as a disease vector. Growers were subsequently pressured to minimize the intrusion of wildlife onto their farm fields by removing surrounding noncrop vegetation. How vegetation removal actually affects foodborne pathogens remains unknown, however. We combined a fine-scale land use map with three datasets comprising ∼250,000 enterohemorrhagic E. coli (EHEC), generic E. coli, and Salmonella tests in produce, irrigation water, and rodents to quantify whether seminatural vegetation surrounding farmland is associated with foodborne pathogen prevalence in California's Central Coast region. We found that EHEC in fresh produce increased by more than an order of magnitude from 2007 to 2013, despite extensive vegetation clearing at farm field margins. Furthermore, although EHEC prevalence in produce was highest on farms near areas suitable for livestock grazing, we found no evidence of increased EHEC, generic E. coli, or Salmonella near nongrazed, seminatural areas. Rather, pathogen prevalence increased the most on farms where noncrop vegetation was removed, calling into question reforms that promote vegetation removal to improve food safety. These results suggest a path forward for comanaging fresh produce farms for food safety and environmental quality, as federal food safety reforms spread across ∼4.5 M acres of US farmland.agriculture | biodiversity | disease ecology | E. coli | foodborne pathogens

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Section: Discussionmentioning

confidence: 97%

Comanaging fresh produce for nature conservation and food safety

Karp

Gennet

Kilonzo

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…An epidemiological study by Strawn et al (22) reported that irrigation of field more than 3 days prior to sample collection reduced the odds of L. monocytogenes isolation from soil and drag swab samples in a produce field. Similarly, our previous study (6) showed that spinach irrigated more than 5 days prior to harvest had nearly 76% lower odds of generic E. coli isolation compared to spinach irrigated 5 days or less prior (OR ϭ 0.24).…”

Section: Discussionmentioning

confidence: 99%

“…Wildlife are well known as carriers of pathogens causing foodborne illnesses. Strawn et al (22) reported that observation of wildlife within 3 days prior to sampling increases odds of L. monocytogenes isolation from soil and drag swab samples in a produce field. Other studies (15,22) have also suggested wildlife are an important source of pathogen transmission to produce.…”

Section: Discussionmentioning

confidence: 99%

“…Strawn et al (22) reported that observation of wildlife within 3 days prior to sampling increases odds of L. monocytogenes isolation from soil and drag swab samples in a produce field. Other studies (15,22) have also suggested wildlife are an important source of pathogen transmission to produce. Nevertheless, to our knowledge, this is the first epidemiological study that was able to show that the extent of microbial contamination (count) on produce could be reduced by using fences to control wildlife intrusion into a produce farm.…”

Section: Discussionmentioning

confidence: 99%

“…Although numerous studies have evaluated farm-related factors influencing the microbial contamination of produce (5,6,(11)(12)(13)(15)(16)(17)(18)(19)(20)(21)(22), only a limited number of studies (16,17,23) examined the bacterial count on produce as affected by risk factors other than the farming type (e.g., organic or conventional farm) (5,12,(18)(19)(20). Surprisingly, to our knowledge, no study has systematically assessed the impact of farm-related factors, including management practices, environment, landscape, and weather factors, on the bacterial count on produce.…”

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confidence: 99%

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Multifactorial Effects of Ambient Temperature, Precipitation, Farm Management, and Environmental Factors Determine the Level of Generic Escherichia coli Contamination on Preharvested Spinach

Park

Navratil

Gregory³

et al. 2015

Appl Environ Microbiol

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A repeated cross-sectional study was conducted to identify farm management, environment, weather, and landscape factors that predict the count of generic Escherichia coli on spinach at the preharvest level. E. coli was enumerated for 955 spinach samples collected on 12 farms in Texas and Colorado between 2010 and 2012. Farm management and environmental characteristics were surveyed using a questionnaire. Weather and landscape data were obtained from National Resources Information databases. A two-part mixed-effect negative binomial hurdle model, consisting of a logistic and zero-truncated negative binomial part with farm and date as random effects, was used to identify factors affecting E. coli counts on spinach. Results indicated that the odds of a contamination event (non-zero versus zero counts) vary by state (odds ratio [OR] ‫؍‬ 108.1). Odds of contamination decreased with implementation of hygiene practices (OR ‫؍‬ 0.06) and increased with an increasing average precipitation amount (mm) in the past 29 days (OR ‫؍‬ 3.5) and the application of manure (OR ‫؍‬ 52.2). On contaminated spinach, E. coli counts increased with the average precipitation amount over the past 29 days. The relationship between E. coli count and the average maximum daily temperature over the 9 days prior to sampling followed a quadratic function with the highest bacterial count at around 24°C. These findings indicate that the odds of a contamination event in spinach are determined by farm management, environment, and weather factors. However, once the contamination event has occurred, the count of E. coli on spinach is determined by weather only. Foodborne disease outbreaks associated with produce impose a considerable public health burden (1). Among different produce commodities, leafy green vegetables have been identified as a group of high concern from a microbiological safety perspective due to their being implicated in multiple outbreaks of foodborne disease with high numbers of illnesses worldwide (2). Indeed, leafy green vegetables are commonly grown in open farm fields, where they may be exposed to microbial contamination from soil, manure fertilizer, irrigation water, and intrusions of wild or domestic animals, and they are likely to be consumed fresh or minimally processed. Enteric foodborne pathogens, such as Salmonella and Escherichia coli O157:H7, have been the main causative agents responsible for foodborne outbreaks associated with leafy green vegetables in the United States (3). These pathogens are spread in the environment through feces of infected animals and humans (4). While contamination of leafy greens with these foodborne pathogens has major consequences (2), fortunately it occurs at a low frequency (5, 6). The low frequency and heterogeneous distribution of these pathogens in the produce field make their detection difficult, costly, and time-consuming. Instead indicator organisms are routinely used by the industry, environmental agencies, and public health organizations to verify effective implementation of good ag...

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Isolation of Listeria monocytogenes from Food and Water: Official and Experimental Protocols

2014

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Listeria monocytogenes is frequently encountered in foods but often at low concentrations and typically in the presence of other microbiota, including nonpathogenic Listeria spp. The potential of L. monocytogenes to cause severe human disease mandates sensitive, accurate, and rapid detection in foods. Isolation of L. monocytogenes from foods is critical, not only for routine surveillance, but also for epidemiologic investigations. Isolation of the pathogen from water (especially surface water used for irrigation) is similarly important, as produce has been implicated in listeriosis outbreaks and contaminated water can be involved in contamination of produce. This unit provides basic protocols for the isolation of L. monocytogenes from foods and water.

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Risk Factors Associated with Salmonella and Listeria monocytogenes Contamination of Produce Fields

Cited by 150 publications

References 61 publications

Comanaging fresh produce for nature conservation and food safety

Comanaging fresh produce for nature conservation and food safety

Multifactorial Effects of Ambient Temperature, Precipitation, Farm Management, and Environmental Factors Determine the Level of Generic Escherichia coli Contamination on Preharvested Spinach

Isolation of Listeria monocytogenes from Food and Water: Official and Experimental Protocols

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