Since April, the Centers for Disease Control has identified more than 1,300 people who became ill after being infected with a strain of Salmonella Saintpaul believed to be linked to consumption of certain varieties of fresh tomatoes. More recently, case-control studies have found evidence that fresh jalapeño and Serrano peppers from Mexico may be implicated in the outbreak as well. Epidemiologist Karin Rosenblatt, a professor in the department of kinesiology and community health at Illinois, discussed the continuing food scare in an interview with News Bureau editor Melissa Mitchell.
What's the process for identifying the source of a salmonella outbreak?
To identify the food involved, investigators at the CDC and state health departments asked people who had been infected with Salmonella Saintpaul what they had eaten one to two days before they became ill and compared their diets with those of people who did not have salmonella to see what foods they might have eaten more of. They identified cases of salmonella as part of the outbreak (that is, from the same source) because the bacteria had the same "DNA fingerprint" (the same genetic code). We are now able to recognize better national outbreaks from the same source because of technologic advances in DNA sequencing.
Why do you think it's taken so long and been so difficult for government health officials to track down a definitive source of infection in this particular case?
First of all, most cases were not identified as being part of the outbreak until two to three weeks after the person became ill - the time it takes for the case to get reported to the CDC and for DNA sequencing. It is hard after that long a period for people to remember exactly what foods they ate in the three days before they became ill. Also, many of the foods implicated - tomatoes and chili peppers - were eaten together, so it was hard to separate out the source of the outbreak.
Information available from the Centers for Disease Control has indicated that there may actually be more than one source for this summer's outbreak, that is, tomatoes and peppers, and/or irrigation water from farms where the food items were grown. Does the fact that there may be multiple sources further complicate this situation?
Although the source of the infection may be one or more farms, when the food comes to a processing center, the foods may be cross-contaminated at the plant, causing multiple foods to become contaminated.
The number of new cases seems to have peaked earlier this summer. Should consumers continue to be concerned and vigilant regarding their food sources and choices?
The FDA is warning consumers to not eat raw jalapeno and Serrano peppers that were grown, harvested or packed in Mexico. Tomatoes, raw peppers from the United States, and commercially canned, pickled or cooked peppers are not implicated in the outbreak at the present time and can be eaten.
Where can consumers learn more about this recent Salmonella Saintpaul outbreak and subsequent investigations seeking to isolate the source of the infections?
To find out more about the investigation of the outbreak, go to the CDC Web site at http://www.cdc.gov/salmonella/saintpaul/. To find out more about the FDA warnings about the foods involved and how to avoid infection, go to http://www.fda.gov/oc/opacom/hottopics/tomatoes.html.