In California, between 1996 and 1998, more than 50% of multi-county outbreaks with confirmed food vehicles were related to alfalfa or clover sprouts.
Researchers from the Los Angeles and California Departments of Heath Services, and the Centers for Disease Control and Prevention, Atlanta, Georgia, USA, therefore examined 5 sprouting shoot-associated outbreaks of salmonellosis, and 1 outbreak of infection with non-motile Shiga toxin-producing E. coli O157 that occurred within the 2-year time period.
Within the study population, 600 patients had culture-confirmed disease and 2 died. The research team estimate however, that the 6 outbreaks caused as many as 22,800 unreported or unconfirmed cases of gastrointestinal illness or urinary tract infection.
In case-control studies, odds ratios for the association between illness and alfalfa sprout consumption ranged from 5.0 to an infinite number, with all being statistically significant.
|Eating raw sprouts - could have made 23,000 people ill|
|Ann Intern Med|
Investigations revealed that only 3 sprout growers were implicated, each producer associated with 2 outbreaks.
Strains of Salmonella detected in the outbreaks were isolated from sprouts supplied by 2 of the growers, and from seeds used by the third.
In all 3 incidences, contamination probably came originally from the seeds, which are usually grown by farmers for agricultural uses.
Seed contamination can arise from irrigation water, fertilizing crops with animal manure, or allowing livestock to graze on crops.
Sprout growers may perpetuate or amplify contamination by not disinfecting seeds prior to sowing or not thoroughly cleaning and disinfecting facilities and equipment.
Since there is currently no reliable way to eliminate all pathogens from the seeds or the growing procedures, the researchers say that children, people with damaged immune systems, and the elderly, should not eat raw sprouts.
Furthermore, they state that consumers who want to decrease their risk for foodborne illness "should avoid eating raw sprouts altogether."