A Shigellosis Outbreak Traced to Commercially Distributed Shredded Lettuce

Abstract

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.

A food-borne outbreak of Shigella sonnei gastroenteritis, Austria, 2008

“…Shigella can grow rapidly in food ingredients held at ambient temperature [21,22] and S. sonnei has been shown to multiply in shredded lettuce and lettuce extract under certain conditions [13]. A wide range of salads have previously been involved in foodborne outbreaks of shigellosis.…”

“…Outbreaks of shigellosis have been associated with crowded conditions and poor personal hygiene, such as in prisons, daycare centers, schools and psychiatric institutions [5][6][7][8][9]. Large-scale outbreaks of foodborne shigellosis have been caused by infected food handlers practicing poor standards of personal hygiene [10][11][12][13]. Information on predominant sources and transmission routes of infections is crucial for targeted prevention of foodborne illnesses, and outbreaks frequently offer the only arena for gaining knowledge.…”

A risk assessment approach for fresh fruits

“…Risk assessment approach for fresh fruits Shigella spp. Kapperud et al 1995;Martin et al 1986;Saddik et al 1985;Davis et al 1988;Tauxe et al 1997;Fredlund et al 1987 Yersinia enterocolitica, Yersinia pseudotuberculosis Catteau et al 1985;Darbas et al 1985a,b;Gola et al 1990;Johannessen et al 2002;Salamah 1993;Tassinari et al 1994;Cavazzini et al 1982Cavazzini et al , 1989Nuorti et al 2004 Escherichia coli (EHEC, Besser et al 1993;Zepeda et al 1995;Odumeru et al 1997;Parish 1997;Tauxe et al 1997;Beuchat 1996;Cavazzini et al 1989;Bell and Kyriakides 1998;Franco et al 1987;…”

Scientific Opinion on the risk posed by pathogens in food of non‐animal origin. Part 2 (Salmonella and Norovirus in leafy greens eaten raw as salads)

“…Good practice includes adequate training as well as both hand washing and toilet facilities which are further considered in Section 12.1.5. The contamination of shredded lettuce with Shigella by a food handler, caused a widespread outbreak in the US (Davis et al, 1988) and illustrates this possibility, although nothing similar has been reported for Salmonella or Norovirus and leafy greens. However, since the excretion of Norovirus by ill persons can be very high (EFSA Panel on Biological Hazards (BIOHAZ), 2012) this represents a risk factor for contamination.…”