American Journal of Epidemiology Vol. 128, No. 6: 1312-1321
Copyright © 1988 by The Johns Hopkins University School of Hygiene and Public Health
research-article |
A SHIGELLOSIS OUTBREAK TRACED TO COMMERCIALLY DISTRIBUTED SHREDDED LETTUCE
1Division of Field Services, Epidemiology Program Office, Centers for Disease Control, assigned to the Texas Department of Health Austin, TX
2Bureau of Epidemiology, Texas Department of Health Austin, TX
3Division of Microbiology, Food and Drug Administration Cincinnati, OH
4Midland City/County Health Department Midland, TX
5Deceased; formerly Ector County Health Department Odessa, TX
6Division of Bacterial Diseases, Centers for Disease Control Atlanta, GA
Davis, H. (CDC, Atlanta, GA 30333), J. P. Taylor, J. N. Perdue, G. N. Stelma, Jr., J. M. Humphreys, Jr., R. Rowntree III, and K. D. Greene. A shigellosis outbreak traced to commercially distributed shredded lettuce. Am J Epidemiol 1988; 128:1312–21.
In the period August 30-October 7, 1986, 347 persons in adjacent west Texas counties (Ector and Midland) contracted culture-confirmed Shigella sonnei gastroenteritis. A case-control study showed an increased risk of acquiring shigellosis in Ector County with eating at outlets of fast-food Restaurant A, and in Midland County with eating at Restaurant B or C. A second case-control study, of persons who had eaten at Ector County outlets of Restaurant A, showed an increased risk of acquiring shigellosis with eating foods containing shredded lettuce and tomatoes, which were served together (odds ratio = 68.8; 95% confidence interval 8.5–293.1). All implicated restaurants received shredded lettuce produced at one lettuce-shredding plant; two implicated restaurants did not receive tomatoes from the lot delivered to other implicated restaurants. The lettuce-shredding plant distributed shredded lettuce and intact lettuce; restaurants that received only intact lettuce were not involved in the outbreak. Investigation at the lettuce-shredding plant suggested that a food handler might have been the source of contamination and that the method of processing might have allowed cross-contamination to occur. In the laboratory, the outbreak strain of S. sonnei multiplied rapidly on shredded lettuce at 22 C and survived on refrigerated shredded lettuce for at least seven days. This outbreak, one of the largest outbreaks of Shigella infections in the United States in the last decade, indicates that a large, geographically widespread shigellosis outbreak can result from contaminated shredded lettuce that is distributed commercially.
diarrhea; disease outbreaks; dysentery, bacillary; food contamination; food microbiology; food-processing industry; Shigella; Shigella sonnei