A listeria outbreak traced to cantaloupes has killed 13 people and sickened 72. It's the second cantaloupe-related incident this year, as the benign-looking orange melon was responsible for an outbreak of Salmonella panama that began in February. The CDC has also reported foodborne illness outbreaks this year from papayas, alfalfa sprouts, bologna, hazelnuts, and turkey (twice). Are foodborne illness outbreaks becoming more common?
Not at all. Between 1996 and 2010, the incidence of foodborne infection actually decreased by 23 percent. Most of that progress, however, occurred in the earlier part of the survey period, and infection rates have remained relatively steady since 2006. It's important to keep these data in perspective. Just 18 of the 2.4 million deaths (PDF) in the U.S. in 2007 were due to foodborne illness. About five times as many people die each year from insect stings as from contaminated food. If you're young and healthy, you're even less likely to die from a bad meal.
While public-health authorities have made substantial progress against food contamination over the past 15 years, a couple of bugs have frustrated them. Salmonella infections have not eased since 1996, and have increased slightly since 2006. Salmonella is a very adaptable pathogen. It can live in the gut of virtually any wild or domesticated species and can thrive in many plants as well. Outbreaks have been traced to poultry, eggs, pork, beef, grapes, and beans, to name just a few. When officials find a way to prevent infections from one food source—for example, by improving sanitation in chicken slaughterhouses—salmonella appears in a new, often completely unexpected, food. Scientists are still trying to figure out how between 2006 and 2009 the bug managed to grow in jars of peanut butter, a high-fat food previously thought inhospitable to bacterial proliferation. There was even a salmonella outbreak traced to marijuana.
There are a couple of other factors at work. The microbes that occur naturally in your gut produce acids that kill salmonella, but antibiotics can decimate your intestinal flora. People used to fight off the infection with ease; now we are somewhat more vulnerable. In addition, many children contract salmonella from their pet reptiles and turtles. The government has made little progress in preventing pet-borne salmonella infections.
The real trending foodborne illness is vibrio. It's much less common than salmonella, but its incidence is up 115 percent since 1996. The most common form of the disease in the United State is Vibrio parahaemolyticus, which is contracted from shellfish. (Vibrio cholerae, which patients usually get from drinking contaminated water, is more common worldwide.) The disease is on the rise because our infrastructure is deteriorating, and sewage keeps leaking into the coastal waters that shellfish inhabit.
Global warming may also be an issue, although scientists haven't yet proved the connection. Vibrio parahaemolyticus doesn't grow well in cold water, which is why people in the Chesapeake Bay know to limit their oyster consumption to months that contain the letter R—that is, anytime but May, June, July, and August. However, warming ocean waters may be lengthening the vibrio season. Epidemiologists are also seeing increased outbreaks of the disease in the Pacific Northwest, a region that used to be too cold for the pathogen to thrive.
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Explainer thanks A.M. Saeed of Michigan State University and editor of Salmonella enterica Serovar Enteritidis in Humans and Animals: Epidemiology, Pathogenesis, and Control, and O. Colin Stine of the University of Maryland.