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

21 August 2001 | Volume 135 Issue 4 | Pages 239-247

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% CIs; 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 O157 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 O157 infection should avoid sprout consumption.

*For members of the Investigation Team, see Appendix.

Author and Article Information

From California Department of Health Services, Berkeley, and Los Angeles County Department of Health Services, Los Angeles, California; and Centers for Disease Control and Prevention, Atlanta, Georgia.

Acknowledgments: The authors thank Carmela Groves, Barbara Brynan, Ken Komatsu, Pamela D. Young, and Ellen Kenney for providing information on patients; Mark Miller, Dennis Tan, Rodney Knight, Sabrina Gilliam, and Stephanie Litwak for conducting patient interviews; Liga Kilman and Eleanor Lehnkering for laboratory support; and Barbara Sanderson for providing information on the history of sprout consumption.

Grant Support: By general public funds through the California Department of Health Services, a state agency.

Requests for Single Reprints: Janet Mohle-Boetani, MD, MPH, Disease Investigations and Surveillance Branch, Division of Communicable Diseases Control, 2151 Berkeley Way, Room 708, Berkeley, CA 94704; e-mail, jmohlebo{at}dhs.ca.gov.

Current Author Addresses: Drs. Mohle-Boetani, Werner, and Vugia, Ms. Minassian, Mr. Bryant, and Ms. Abbott: Disease Investigations and Surveillance Branch, Division of Communicable Diseases Control, 2151 Berkeley Way, Room 708, Berkeley, CA 94704.

Dr. Farrar: California Department of Health Services, Food and Drug Branch, 601 North 7th Street, Sacramento, CA 94234.

Dr. Slutsker: Centers for Disease Control and Prevention, 1600 Clifton Road, Mailstop F-22, Atlanta, GA 30333.

Author Contributions: Conception and design: J.C. Mohle-Boetani, J.A. Farrar, S.B. Werner, D. Minassian, D.J. Vugia.

Analysis and interpretation of the data: J.C. Mohle-Boetani, J.A. Farrar, S.B. Werner, D. Minassian, R. Bryant, D.J. Vugia.

Drafting of the article: J.C. Mohle-Boetani, J.A. Farrar, D.J. Vugia.

Critical revision of the article for important intellectual content:

J.C. Mohle-Boetani, J.A. Farrar, S.B. Werner, D. Minassian, L. Slutsker, D.J. Vugia.

Final approval of the article: J.C. Mohle-Boetani, S.B. Werner, D. Minassian, D.J. Vugia.

Provision of study materials or patients: D. Minassian, R. Bryant.

Statistical expertise: D. Minassian.

Administrative, technical, or logistic support: S.B. Werner, D. Minassian, R. Bryant, S. Abbott, L. Slutsker, D.J. Vugia.

Collection and assembly of data: J.C. Mohle-Boetani, J.A. Farrar, D. Minassian, S. Abbott.