A new CDC Vital Signs Report on Food Safety points once again to a stubborn problem: that food can sometimes bite back and be deadly. We would be wise to heed its reminder—that more progress is needed to protect people and drive down foodborne illnesses in the United States and globally. Acting globally means sharing solutions and resources throughout the world to make food safer.
I started in CDC’s “foodborne” group as an EIS officer in 1983. It’s sort of a liberal arts education in pubic health since foodborne diseases can be caused by so many different organisms. Even in the US where our food supply is one of the safest in the world, foodborne illness affects everyone, with 48 million illnesses estimated just in the US—that’s roughly 1 in 6 people.
My experience over the years shows well how understanding the mechanisms by which foods become contaminated in the first place is critical to devising effective control measures. Careful initial interviews with a group of patients are critical to suggest a testable hypothesis, which may point to new food vehicles.
New and Changing Foods…New and Changing Threats
The story of foodborne diseases in the last few decades has been one of a broadening diversity of foods. Take Listeria, one of the most deadly foodborne germs found in food. It also has a penchant for striking hard at pregnant women and their babies, older adults and people with weakened immune systems. Outbreaks in the 1990s were primarily linked to deli meats and hot dogs. Now, Listeria outbreaks are mainly caused by soft Mexican-style cheeses like queso fresco and other soft cheeses that were either made from unpasteurized milk or that got contaminated during cheese-making. Our Listeria report shows that Hispanic ethnicity was common in pregnancy-associated cases (43%). More consumption of Mexican-style soft cheese, like queso fresco, may explain the higher rates among Hispanics. Some outbreaks have also been linked to foods that people may not think of as risky for Listeria, like celery, sprouts, and cantaloupe.
Other germs, like Salmonella, one of the most common germs found in food, has been linked to foods from around the globe as well as right here in the US. We have tracked outbreaks from raw scraped tuna imported from India, mangoes from Mexico, peanut snacks from America, and pinenuts from Turkey. There is E. coli from frozen snacks, raw sprouts, organic spinach and spring mix, apple cider, as well as from the beef and venison; and the rare parasite Cyclospora from imported raspberries.
One of my favorite investigations was during my EIS training when my mentor, Paul Blake, sent me to investigate an epidemic of cholera in Mali, along with Dr. Scott Holmberg. Mali was already in the throes of a drought and then suffered a huge cholera epidemic. In between conducting training sessions on treatment and getting supplies of oral rehydration solution to afflicted areas, we were able to document a mechanism for the apparent but paradoxical link between cholera and drought. In a small village, we used the case-control method to show that those who were stricken with cholera had typically eaten steamed millet gruel, while those who remained well had no millet left and were reduced to eating the tough leaves of a bush that were the local famine food. The millet was eaten in large communal bowls and often was held over from one day to the next for the morning meal.
We knew that steamed rice would support the growth of V. cholerae, so the millet seemed a likely vehicle. But why had cholera appeared only now in central Mali, transmitted through a traditional food? The local custom was to add fermented goats’ milk yogurt to the millet. However, because of the drought, the goats had ceased to give milk and so yogurt was unavailable. Could that have changed the millet? I brought millet back to Atlanta, located a Nubian goat herd, made some fermented milk, and replicated the traditional and famine recipes in the lab. Millet by itself had a neutral pH, but millet made with the goat yogurt had a low pH, low enough to rapidly eliminate V. cholerae. Thus, we speculated that when the drought came, a traditionally safe food became unsafe. Capturing that difference taught us that acidifying food might be an important prevention step for cholera.
Getting food to your table is a complex process. Food goes through many stages and touches countless people before it reaches you. Once food becomes contaminated, germs and infection can spread rapidly through families or between continents.
We all deserve healthy, safe foods, yet many countries lack basic laboratory, and public health resources to identify, track, and stop the spread of foodborne illnesses. Hunting down the foodborne sources of diarrheal disease requires epidemiologists, laboratorians, and sanitarians to regularly communicate with each other and share findings.
In 2000, after a WHO survey showed that many countries lacked basic laboratory and public health resources to detect foodborne diseases, WHO, CDC and partners developed the Global Foodborne Infections Network. Together with CDC’s PulseNet International, these worldwide organizations help countries to strengthen their ability to detect and control foodborne and enteric (gastrointestinal) diseases.
Finding and stopping outbreaks linked across the global will take all of us working together to think locally and act globally and find more recipes for food safety that can outpace diseases spread by contaminated foods.