An Outbreak of Shigellosis Associated with the Consumption of Raw Oysters

Abstract

We describe an outbreak of Shigella sonnei infection among 24 persons who had eaten raw oysters in restaurants in southeastern Texas within five days before the onset of symptoms. The oysters in all eight restaurants were supplied by the same dealer, but examination of a routine water sample collected six days before the probable time of contamination showed the waters where the oysters were harvested to be free of fecal contamination, making widespread sewage contamination unlikely. The suspect oysters were traced to a single boat. Stool swabs from that boat's oyster harvesters allowed the identification of one asymptomatic carrier who had a strain of S. sonnei (determined by colicin typing, plasmid analysis, and testing for susceptibility to antibiotics) that was similar to or the same as that infecting the patients. Although the source of this man's infection was unknown, he reported having eaten no oysters. Investigation revealed that 5-gallon (19-liter) pails were used as toilets aboard the oyster boats. Sewage collected in these pails was often dumped overboard into the harvesting area. We conclude that this outbreak of S. sonnei resulted from poor sanitary procedures that probably allowed stool from a carrier to contaminate oysters either just before or after they were taken aboard the boat.