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Outbreak News

Too Early to Know 'Root Cause' of Listeria Outbreak

Food Safety News

by Dan Flynn

Sep 29, 2011

The nation's top disease trackers and food regulators say it's too early for them to know the "root cause" of the deadly cantaloupe Listeria outbreak, which they expect to worsen in terms of the number of cases and deaths.

Dr. Thomas R. Frieden and Dr. Margaret Hamburg, respectively the director of the Centers for Disease Control and Prevention (CDC) and the commissioner of the U.S. Food and Drug Administration (FDA) took questions about the outbreak from the media in a conference call Wednesday.

The top CDC/FDA brass, along with Dr. Barbara Mahon, deputy director of the enteric disease branch at CDC, and Dr. Sherri McGarry, senior advisor to FDA's office of foods, answered reporters' questions for about an hour.

"Listeria is a rare but deadly disease," Frieden said. He cautioned people not to eat the cantaloupe they may have in their refrigerators if they don't know where it came from.

"If you know the cantaloupe that you have is not Jensen farms, then it's OK to eat. But if you're in doubt, then throw it out," he said, referring to the Colorado farm at the center of the nation's deadliest food poisoning outbreak in more than a decade.

Because the Listeria bacteria that can cause infection can have a relatively long incubation period, the CDC expects to see both the number of outbreak cases and fatalities continue to rise into October. Currently, 13 deaths among 72 cases have been confirmed, and at least three more deaths in Kansas, Wyoming and New Mexico may be part of the outbreak.

Frieden said two of the case patients are pregnant women who are recovering.

Frieden also explained what sets Listeria apart from other common foodborne pathogens.

"Listeria is an unusual bacteria in a couple of ways," he said. "One is that the -- what's called the incubation time, the time between which -- between when you consume it and when you get sick, is longer than it is for many other bacteria. It can be one to three weeks. It can even be two months or more in some cases. So people who consumed the cantaloupe some time ago may continue to develop illness in the coming days and weeks. So we do anticipate that there will be a rising number of cases in the days and weeks to come.

"Also, it's unusual in that it flourishes even in the cold. So unlike most other bacteria, if you got a contaminated cantaloupe in your refrigerator, that -- the Listeria in the cantaloupe -- will continue to grow in your refrigerator. That's unusual. That's not what we see with Salmonella or other bacterial infections, and it's one of the reasons that we unfortunately may see a continued number of cases from cantaloupe that are already in people's refrigerator now over the coming days and weeks."

McGarry said CDC and FDA are working with the state of Colorado on a "root cause" analysis at Jensen Farms, where the contaminated cantaloupes were grown, to see if they can pinpoint how this problem developed.

"To really get at the heart of what may have happened to cause this contamination, and not just how it may have been contaminated, but was there any opportunity for continued growth or spreading of that contamination," McGarry said. "So what we basically are doing is we will look at various parameters, environmental in particular, that may have contributed to that contamination and spread.

"And some of those things that we'll be looking at is any potential animal intrusion. We'll be looking at water quality. We'll be looking at the growing practices, the harvesting practice," she added. "We'll also be looking at the process within the facility for packing and potentially rinsing the cantaloupes themselves and how they were stored and whether there's amplification in that process. So we'll be looking at different factors from the environmental perspective to see how this contamination may have occurred, how it could have been spread.

"And then, most importantly, we're going to take these lesson learned, share that with our partners and industries, CDC and the states, and what we want to do is we want to really prevent this from happening in the future. And again, that's quite consistent with the (new) Food Safety Modernization Act. And that's our goal here is to prevent future outbreak (in) this particular situation."

Hamburg defended FDA's policy of asking consumers to find out on their own whether their grocery store carried the bad melons. The agency has not made a list of retailers available as USDA's Food Safety and Inspection Service (FSIS) does when a pathogen contaminates meat.

"I think it's a lot more accurate for the consumer to actually ask their retailer in terms of the ability to get that information out and, of course, when you put stuff on the website, not everybody accesses it," the commissioner said. "So I think it is an important message that if people are uncertain to ask their retailer. That's how they'll get the most accurate and most direct information."

"Rocky Ford" cantaloupes grown by Jensen Farms were also exported, the regulators said. The FDA officials said they did not have list of countries handy, but all foreign governments were notified about the Listeria outbreak.

The FDA officials also said they did not know the total number of cantaloupes involved in the recall. (Later on Wednesday, a spokesman for Jensen Farms said at least 1.5 million cantaloupes, Jensen Farms' entire 2011 harvest, have been recalled because of the potential Listeria contamination.)

While cantaloupes have previously been contaminated by other pathogens, this is the first time the melons have been known to carry Listeria.

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