Concurrent Outbreaks of Shigella sonnei and Enterotoxigenic Escherichia coli Infections Associated with Parsley: Implications for Surveillance and Control of Foodborne Illness†

Abstract

In recent years, the globalization of the food supply and the development of extensive food distribution networks have increased the risk of foodborne disease outbreaks involving multiple states or countries. In particular, outbreaks associated with fresh produce have emerged as an important public health concern. During July and August 1998, eight restaurant-associated outbreaks of shigellosis caused by a common strain of Shigella sonnei occurred in the United States and Canada. The outbreak strain was characterized by unique pulsed-field gel electrophoresis patterns. Epidemiologic investigation determined that the illness was associated with the ingestion of parsley at four restaurants; at the other four restaurants, the majority of the people who contracted the illness ate parsley. Isolates from patrons in two unrelated restaurant-associated enterotoxigenic Escherichia coli (ETEC) outbreaks in Minnesota shared a common serotype and pulsed-field gel electrophoresis (PFGE) pattern. Parsley was the implicated or suspected source of both ETEC outbreaks. In each of the outbreak-associated restaurants, parsley was chopped, held at room temperature, and used as an ingredient or garnish for multiple dishes. Infected food workers at several restaurants may also have contributed to the propagation of the outbreak. The sources of parsley served in outbreak-associated restaurants were traced, and a 1,600-acre farm in Baja California, Mexico, was identified as a likely source of the parsley implicated in six of the seven Shigella outbreaks and as a possible source of the parsley implicated in the two ETEC outbreaks. Global food supplies and large distribution networks demand strengthened laboratory and epidemiologic capacity to enable state and local public health agencies to conduct foodborne disease surveillance and to promote effective responses to multistate outbreaks.