Alfalfa Sprouts and Salmonella Kottbus Infection: A Multistate Outbreak following Inadequate Seed Disinfection with Heat and Chlorine

Abstract

Raw sprouts have been implicated in a number of foodborne disease outbreaks. Because contaminated seeds are usually responsible, many sprout producers attempt to disinfect seeds before germination and detect sprout contamination during production. In March 2001, we detected an increased number of Salmonella serotype Kottbus isolates in California. Overall, we identified 31 cases from three western states. To identify the cause, we conducted a case-control study with the first 10 identified case-patients matched to 20 controls by age, sex, and residential area. Our case-control study found illness to be statistically associated with alfalfa sprout consumption. The traceback investigation implicated a single sprouter, where environmental studies yielded Salmonella Kottbus from ungerminated seeds and floor drains within the production facility. Pulsed-field gel electrophoresis patterns of all patient, seed, and floor drain Salmonella Kottbus isolates were indistinguishable. Most implicated sprouts were from seeds that underwent heat treatment and soaking with a 2,000-ppm sodium hypochlorite solution rather than the Food and Drug Administration (FDA)-recommended 20,000-ppm calcium hypochlorite soak. Other implicated seeds had been soaked in a calcium hypochlorite solution that, when tested, measured only 11,000 ppm. The outbreak might have been averted when screening tests of sprout irrigation water detected Salmonella in January; however, confirmatory testing of these samples was negative (but testing improperly utilized refrigerated irrigation water). Producers should use the enrichment broth of positive screening samples, not refrigerated irrigation water, for confirmatory testing. Until other effective disinfection technologies are developed, producers should adhere to FDA recommendations for sprout seed disinfection.

Monte Carlo Simulation of Pathogen Behavior during the Sprout Production Process

“…In contrast to these results, a traceback investigation of a Salmonella serovar Kottbus outbreak in 2001 was able to isolate the pathogen from ungerminated seeds, although methods were not reported, so further comparison with our results is not possible (58). Similarly, experiments utilizing naturally contaminated seeds from a S. enterica serovar Mbandaka outbreak were able to isolate the pathogen from 67% of 100-g samples by conventional methods and from 72% of samples by molecular methods (50).…”

“…One method of disinfection involved heating seeds, cooling them with well water, and then exposing them to a 2,000 ppm sodium hypochlorite soak for 15 min. Alternatively, seeds were treated with 20,000 ppm chlorine for 15 min, although records could not verify whether the concentration was actually 20,000 ppm (58) . FIG.…”

“…Relevant literature was grouped into two main subject categories: growth of pathogens during sprouting (1,8,16,19,33,41,42,47,49) and pathogen detection on seeds or sprouts (8,15,20,21,23,36,45,48,55,59). Epidemiological literature was reviewed to assemble a comprehensive understanding of primary risk factors in the sprouting process (3,4,9,25,29,30,35,37,52,53,58). Data on processes not currently used in sprouting operations were not included in our model (10, 12, 13, 18, 27, 34, 38, 39, 42-44, 54, 56).…”

“…Reported outbreaks have increased steadily in the intervening decades (32). Despite increased awareness, outbreaks continue unabated (28,58).…”

Influence of Pressure on Germination of Garden Cress, Leaf Mustard, and Radish Seeds at Various Temperatures

“…Several methods have been proposed for reducing microbial counts [1][2][3][4][5][6][7][8], but none of them completely eliminate pathogens inside seeds. High hydrostatic pressure treatment has been studied as a new approach [9,[10][11][12][13][14][15].…”