December 2, 2005
Outbreaks, Dissertation work, and Sprouts
An e-mail newsletter in my Inbox today contained links to two stories. The first story described a recent study by the Center for Science in the Public Interest concluding that produce contributed to more illnesses than poultry, eggs, and other animal products. CSPI studied reports of food-related outbreaks and noted the implicated foods that were the source of the disease-causing organisms.
This report comes at a very influential time in the food safety arena and it raises exactly the questions I am tackling in my dissertation work. There's a great interest in these types of attribution studies that seek to learn where foodborne illness cases are coming from. What types of foods are contributing most to the burden of disease?
But what we really want to know isn't just "what" but also "how" and "where." How are these foods becoming contaminated? Where in the food production, transportation, and preparation steps is this contamination occurring?
In outbreak investigations, the point of contamination can sometimes be difficult to discern. Produce may have been contaminated in preparation, often cross-contaminated from other foods in the kitchen. But there are increasing numbers of multi-state outbreaks where cases crop up in multiple places at about the same time. In these instances, it seems most likely that the implicated food was contaminated on the farm or during processing or shipping. This is where our ability to conduct trace-back investigations is key to solving the mystery of exactly where and how, and, hopefully, preventing similar contamination in the future. CSPI is lobbying for better record-keeping and ID tagging of foods to help in these efforts.
Another difficulty is lack of data. This study looked at outbreaks that had both an identified pathogen -- the bacteria, virus, toxin, or parasite was recovered -- and an identified source -- there was conclusive evidence that pointed to a food. But what about the unknown and unidentified? What about the people who become ill and never see a doctor and don't get tested? We don't have great data on the food side, either -- especially produce where no routine testing is done.
My work is to identify the first two of Sec. Donald Rumsfeld's information trilogy -- the known knowns, the known unknowns, and the unknown unknowns -- and give an account of where our knowledge lies in attributing Salmonella cases to foods at the point of production. [Secretary Rumsfeld got a lot of ribbing after that news briefing, but I've found his words very useful in my work and explaining my work to others!]
The other story in that e-mail relates more to a personal joke than the actual news item. The story is about a recent Salmonella outbreak in Ontario from mung bean sprouts. There have been several Salmonella outbreaks from various types of sprouts in the past decade or so. One of the difficulties in preventing these outbreaks is that Salmonella can contaminate the sprout seed itself, as well as during the growing phase.
The joke here is that I'd heard extensive accounts of these sprout-associated outbreaks from one of my major professors, Dr. Craig Hedberg. We'd worked closely on several food safety projects when I first arrived at the U of M. One time when we were on our way to a meeting off campus, we stopped for lunch at a little sandwich shop. I ordered the veggie special but told them to "hold the sprouts." Craig's eyebrow shot up, he gave a wry smile and said, "Don't do that on my account." I gave a snort and replied that if not on his account -- foodborne disease expert, veteran outbreak investigator -- than whose? And I'm not the only one. Our entire department, it seems, is sprout averse from Craig's stories. So, you see why I smiled when I saw that headline today. Craig is now over in Paris for a year, working with French officials on improving their foodborne disease surveillance. I have to wonder if he's sitting in a little French cafĂ© at this moment, regaling his company with similar stories.