Escherichia coli O157 and Salmonella Infections Associated with Sprouts in California, 1996–1998

Background: In California, from 1996 through 1998, more than 50% of multicounty outbreaks with confirmed food vehicles were related to alfalfa or clover sprouts. Objective: To summarize investigations of sprout-associated outbreaks. Design: Matched case-control studies. Setting: California. Patients: Outbreak-associated patients and matched population controls. Measurements: Matched odds ratios and 95% Cls; traceback and environmental investigations of sprout and seed growers; and pulsed-field gel electrophoresis of isolates from patients, sprouts, and seeds. Results: Five sprout-associated outbreaks of salmonellosis and one outbreak of infection with nonmotile Shiga toxin-producing Escherichia coli 0157 occurred. Six hundred patients had culture-confirmed disease, and two died. It is estimated that these outbreaks caused 22 800 cases of gastrointestinal illness or urinary tract infection. In the case-control studies, odds ratios for the association between illness and alfalfa sprout consumption ranged from 5.0 to ∞ (all were statistically significant). Three sprout growers were implicated, and each was associated with two outbreaks. Outbreak strains of Salmonella were isolated from sprouts supplied by two sprout growers and from seeds used by the third sprout grower. Conclusions: As currently produced, sprouts can be a hazardous food. Seeds can be contaminated before sprouting, and no method can eliminate all pathogens from seeds. Seed and sprout growers should implement measures to decrease contamination. The general public should recognize the risks of eating sprouts, and populations at high risk for complications from salmonellosis or E. coli 0157 infection should avoid sprout consumption.