Prevalence of Escherichia coli O157:H7 and Salmonella on Inshell California Walnuts

Abstract

Inshell walnuts collected from California walnut handlers over four harvests were evaluated for the presence of Escherichia coli O157:H7 and Salmonella. E. coli O157:H7 was not detected in any of 2,903 375-g samples evaluated in 2011, 2012, and 2013 (<0.034% prevalence; 95% confidence interval [CI], 0 to 0.13%). Salmonella was not isolated from any of the 935 samples in 2010 (100 g evaluated; <0.11% prevalence; 95% CI, 0 to 0.41%) but was isolated from 2 of 905 (375 g; 0.22% prevalence; 95% CI, 0.061 to 0.80%), 1 of 998 (375 g; 0.10% prevalence; 95% CI, 0.018 to 0.56%), and 1 of 1,000 (375 g; 0.10% prevalence; 95% CI, 0.018 to 0.56%) samples in 2011, 2012, and 2013, respectively, for an average annual prevalence of 0.14% (375 g; 95% CI, 0.054 to 0.35%). The levels of Salmonella in positive samples determined by a modified most-probable-number (MPN) method were estimated to be 0.32 to 0.42 MPN/100 g (95% CI, 0.045 to 3.6 MPN/100 g).

Survey of Salmonella in raw tree nuts at retail in the United States

“…This might also indicate that the industry is working effectively to reduce pathogens in their products under the influence of Food Safety Modernization Act (FSMA). The FDA prevalence data were similar to limited published reports (Brar et al., 2016; Danyluk et al., 2007; Davidson et al., 2015; Eglezos, Huang, & Stuttard, 2008; Harris et al., 2016; Little et al., 2009) on Salmonella contamination of different varieties of tree nuts as summarized in our recent publication (Zhang, Hu, Melka, et al., 2017). When comparing the prevalence of Salmonella among different surveys, readers need to take consideration of differences in collection points, sample sizes, and detection methodologies used in different studies.…”

“…Similar Salmonella population estimates in positive tree nut samples were observed in the previous similarly structured survey, where 60.7% of Salmonella ‐positive tree nuts samples had Salmonella below the limit of detection of 0.003 MPN/g, 25% had 0.003 to 0.005 MPN/g, and the highest was 0.092 MPN/g (Zhang, Hu, Melka, et al., 2017). Similar results have been reported for surveys of nut commodities including almonds, peanuts, pecans, walnuts, and pistachios (Brar et al., 2016; Calhoun et al., 2013; Danyluk et al., 2007; Davidson et al., 2015; Harris et al., 2016). An estimate of 8.5 MPN/100 g has been reported for recalled raw almonds associated with a Salmonella outbreak (Danyluk et al., 2007).…”

“…Low‐water‐activity foods, such as tree nuts and peanuts, do not have the favorable characteristics for bacterial growth. However, Salmonella has been detected in almonds, cashews, hazelnuts, macadamia nuts, peanuts, pecans, pine nuts, pistachios, and walnuts in the past worldwide (Bansal, Jones, Abd, Danyluk, & Harris, 2010; Bedard, Kennedy, & Weimer, 2014; Blessington, Theofel, Mitcham, & Harris, 2013; Brar, Strawn, & Danyluk, 2016; Calhoun, Post, Warren, Thompson, & Bontempo, 2013; Danyluk et al., 2007; Davidson, Frelka, Yang, Jones, & Harris, 2015; Little, Jemmott, Surman‐Lee, Hucklesby, & De Pinna, 2009; Miksch et al., 2013; Zhang, Hu, Melka, et al., 2017). Salmonella has been shown to survive for a long period of time on tree nuts at ambient temperature (Abd, McCarthy, & Harris, 2012; Frelka, Davidson, & Harris, 2016; Kimber, Kaur, Wang, Danyluk, & Harris, 2012; Santillana Farakos, Pouillot, & Keller, 2017).…”

Prevalence and Amounts of Salmonella Found on Raw California Inshell Pistachios

“…The average prevalence of Salmonella in sinker pistachios of 0.37% (100 g; 95% CI, 0.21 to 0.67%) was significantly lower than that determined in raw almond kernels and raw inshell pecans and was not significantly different from that in raw inshell walnuts. The average prevalence of Salmonella was 0.98% (100 g; 95% CI, 0.83 to 1.2%; 137 of 13,972) in raw almond kernels (8, 17, 25), 0.95% (100 g; 95% CI, 0.70 to 1.3%; 44 of 4,641) in raw inshell pecans (10), and 0.14% (375 g; 95% CI, 0.054 to 0.35%; 4 of 2,903) in raw inshell walnuts (18).…”

“…With the exception of almonds (8,17), pecans (10), and walnuts (18), very little is known about the prevalence, levels, and distribution of Salmonella in tree nuts collected before retail distribution; these data are important for development of quantitative microbial risk assessments and of scientifically sound product sampling schemes for verification of food safety plans. Three retail market surveys have included pistachios of unknown origin.…”