Prevalence and levels of Shiga toxin-producing Escherichia coli and Salmonella in California raw almond kernels from the 2021 harvest compared with data from harvests between 2001-2013.

The prevalence and levels of pathogens in foods are critical inputs for quantitative microbial risk assessment. This study aimed to determine the prevalence, levels, and distribution of Escherichia coli O157:H7, non-O157 Shiga toxin-producing (STEC), and Salmonella on raw almond kernels from the 2021 California harvest, and to compare the results with data from 2001-2013. During the 2021 harvest, 1-2 kg samples were collected at processing facilities from 601 incoming single-variety almond lots representing 15 varieties. Each lot was tested for presence of E. coli O157:H7 and STEC using 375-g subsamples and for Salmonella using 100-g subsamples. Aerobic plate count (APC) and levels of coliforms, Enterobacteriaceae, yeasts, and molds were determined for a subset of positive and negative lots. Salmonella levels in positive lots were estimated using a modified three-tube most-probable-number (MPN) method with additional 25- and 50-g subsamples processed through sample depletion. A subset of Salmonella-negative lots was also retested using multiple 100-g subsample enrichments. None of the 601 lots was positive for either E. coli O157:H7 or STEC. Salmonella was isolated from 18 lots (3.0% [95% CI, 1.8 to 4.7%]), a higher prevalence than the 9-year average from earlier surveys (0.98% [95% CI, 0.83 to 1.2%]). Estimated Salmonella levels in 2021 ranged from 0.0016 to 0.011 MPN/g (mean 0.0034 ± 0.0023 MPN/g), consistent with 2001-2013 levels (mean 0.012 ± 0.017 MPN/g; range, 0.00020-0.15 MPN/g). Whole-genome sequencing of 2021 isolates identified Salmonella enterica subspecies arizonae, diarizonae, and enterica, including nine Salmonella enterica subspecies enterica serovars. No significant differences (P > 0.05) in APC or levels of yeasts, molds, coliforms, or Enterobacteriaceae were observed between Salmonella-positive and -negative lots in 2021, consistent with findings from earlier surveys. Salmonella detection was not associated with almond variety.