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Emerging Pathogens: Listeria Threatens a Growing Senior Population

From August through October 2011, 147 people in 28 states were infected with Listeria monocytogenes after eating cantaloupe from Jensen Farms in Colorado. There were 33 deaths, and one pregnant woman had a miscarriage as a result, making it one of the deadliest outbreaks of foodborne illness in the U.S. in recent years.

Apart from some diarrhea or minor gastrointestinal problems, most people don’t get sick when they’re exposed to Listeria. But, if the pathogen gets into their bloodstream, it can cause listeriosis, a disease that kills one out of every five victims. Because of these odds, Listeria has the highest mortality rate of foodborne pathogens.

Groups most at risk for Listeria infections are older adults, pregnant women and people with an underlying medical conditions such as cancer, liver or kidney disease, diabetes or HIV/AIDS.

People 65 and older are four times more likely to get sick from Listeria poisoning than the general population, and pregnant women – who may not develop listeriosis themselves but whose babies could be threatened – are 10 times more likely.

While it’s important to remember that there are only about 800 laboratory-confirmed cases of Listeria in the U.S. each year, more than half of them occur among older adults. In the 2011 cantaloupe-related outbreak, most of the cases involved people older than 60, and those who died were between the ages of 48 and 96.

“Typically, when the highly susceptible populations are infected, they’re the ones that experience the most severe symptoms and often the high mortality rates,” said Michael Doyle, director of the Center for Food Safety. “As we age, we need to be more careful about the types of foods we eat. That means making sure that foods that are likely to be contaminated with harmful microbes should be cooked or somehow processed or treated to ensure safety. We should not be taking the risks that maybe younger people would take – eating less well-cooked meat, for example.”

Foods that typically cause Listeria outbreaks are Mexican-style soft cheeses made with unpasteurized milk, deli meats, and hot dogs. Produce was not often identified as a source in the past, but sprouts caused an outbreak in 2009, and pre-cut celery caused an outbreak in 2010.

“There have been a lot of successes on the ready-to-eat meat front,” said Alicia Cronquist, an epidemiologist with the Colorado Department of Public Health and Environment who investigated the 2011 outbreak. “Manufacturers have put in enormous efforts, and we’ve seen a real decline in outbreaks due to those deli meats and poultry products.”

Doyle agrees and says this is why he’s not as concerned about lunch meats now as he is about fresh produce.

“I am very concerned about fruits and vegetables – not just because of Listeria, but because we’ve had hiccups with a lot of other pathogens with fresh fruits and vegetables,” he said.

“We frequently identify new vehicles when we do outbreak investigations, whether it’s Listeria, E. coli or Salmonella,” Cronquist said. “This outbreak was very unusual in that it was huge and had a terrible number of fatalities, but it was also notable in that [cantaloupe] was a novel Listeria vehicle.”

In addition to its high mortality rate, Listeria is an unusual foodborne pathogen because it can survive and multiply at refrigerator temperatures. In order to avoid Listeria, CDC recommends that high-risk consumers heat hot dogs, lunch meats and cold cuts to an internal temperature of 165 degrees F and avoid products with unpasteurized milk, refrigerated paté or meal spreads, and uncooked smoked seafood.

When it comes to melon safety, consumers and food preparers should wash their hands before and after handling a whole melon, scrub the outside of melons under running water and dry them with a clean cloth or paper towel before cutting, and then promptly consume or refrigerate cut melon and keep it for no more than a week.

FDA has also released “Food Safety for Older Adults” to address threats from all major pathogens and offer prevention tips for seniors. Because, as Doyle says, “It’s the elderly that are going to be more susceptible to all these different pathogens, not just Listeria. They’re the ones that are going to suffer the most severe consequences.”

© Food Safety News
  • Dale Hogue

    Why should I worry? I don’t eat fruit or vegetables or any of the other stuff that we’ve been told is good for us. Why? Because I eat stuff that that “they” tell me isn’t good for me. It’s worked for more than 83 years, so why should I break a bad habit just so I can get poisoned by eating healthy foods?