Foodborne disease in our global village: A multinational investigation of an outbreak of Salmonella serotype enteritidis phage type 4 (SE PT4) infections in Puerto Vallarta, Mexico

Background: In late 1996, a multinational investigation was launched following an outbreak of diarrheal illness which caused the early termination of an international scientific conference at a first-class hotel in Mexico. Methods: A questionnaire was mailed to all American and selected international attendees. A case was defined as an illness with ≥3 loose stools during a 24-hour period in a conference attendee or accompanying family member, with illness lasting >2 days and onset between November 6 and 9, 1996. Results: Questionnaires were returned by 81% (232/288) of American attendees, 47% (18/38) of international attendees, and 25 family members; 30% (83/275) respondents met the case definition. Ill persons resided in 7 countries. SE PT4 was isolated from stool specimens from patients in Canada, the United Kingdom, and the United States. Isolates were indistinguishable by pulsed-field gel electrophoresis from other SE PT4 isolates from American visitors to Mexico. Attending a hotel banquet on November 6 was associated with illness; 42% (82/194) of banquet attendees became ill versus 3% (1/37) of non-attendees (relative risk [RR]=15.6, 95% confidence interval [CI]=2.3-108.9). The only banquet food item associated with illness was chili rellenos; 53% (58/110) of persons who ate chili rellenos were ill versus 22%(12/55) of those who did not (RR=2.4, 95% CI=1.4-4.1). Chili rellenos ingredients included eggs and cheese; Salmonella was isolated from the cheese but the isolate was not serotyped. Conclusion: SE PT4 is a cause of travelers' diarrhea and can cause outbreaks even among travelers who follow routine precautions (i.e., staying in a first-class hotel and eating hot foods). International collaboration in investigating similar outbreaks, including sharing subtyping results (e.g., PFGE), will be necessary for long-term prevention.