CDC Reports Investigative Techniques Used to Isolate Source of Mexican-Style Fast Food Salmonella Enteritidis Outbreak
The Centers for Disease Control and Prevention (CDC) has released a report detailing the processes involved in isolating the source of the recent (October 2011-January 2012) outbreak of Salmonella strain Enteritidis.
The process involved cooperation between agencies at the federal, state, and local levels. These efforts resulted in the CDC’s conclusion that the outbreak was related to the consumption of food from a Mexican-style fast food restaurant chain. The agency has yet to identify the name of the chain, and is instead calling it “Restaurant Chain A.”
Of the 68 individuals who have been linked to the strain of Salmonella involved in the outbreak, the CDC had access to the data for 52 individuals. Of those persons, 60% reported eating at the implicated restaurant chain within 7 days of becoming ill. To contrast with the general population, among other individuals who did not become ill, only 17% reported eating at “Restaurant Chain A” in the week before illness onset – a very stark difference in figures. Further, the CDC released that 3 individual franchises (locations) were involved in more than one case of outbreak-related illness.
Due to the common ingredients used in menu items at the restaurant chain, the CDC was unable to identify a specific food as the source of illness. However, the report does include the following figures: of the individuals who fell ill (for whom data were available), 94% reported eating ground beef, 90% reported eating lettuce, 77% reported eating cheese, and 35% reported that they consumed tomatoes.
Despite the fact that the most commonly reported ingredient was beef, the CDC says that the epidemic curve in this outbreak is “consistent with those observed in past produce-related outbreaks” because of the sharp increase and subsequent decline in illnesses reported over the span of one to two months. The CDC further opined that ground beef was “an unlikely source due to the handling and cooking processes used” by the restaurant chain.
The US Food and Drug Administration (FDA) attempted to use information about supply truck delivery routes and schedules – including various shipping records of suspected and other foods to the restaurant locations – to identify the exact food source of the outbreak. The franchise locations associated with more than one outbreak case were located on two different shipping routes, and comparison of the lists of suspected foods received by these locations didn’t show any commonalities across a number of different suppliers.
The outbreak has been associated with 68 cases of Salmonella Enteritidis across 10 states, with the majority of cases reported in Texas (43) and Oklahoma (16).
