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Listeria in Smoked Salmon: Examining the Risk

Listeria monocytogenes bacteria detected in some ready-to-eat smoked salmon samples sparked a rash of recalls in recent months, with major fish producers such as Ocean Beauty, Marine Harvest and Pacific Seafood Group, plus retail giants including Whole Foods Market, Walmart and Ralph’s, getting caught in the recall net.

But no outbreak of illnesses prompted these companies to voluntarily pull smoked salmon from store shelves.

The uptick in recalls led some to speculate that the U.S. Food and Drug Administration (FDA) might be taking a new get-tough approach targeting Listeria in smoked salmon and stepping up inspections.

smoked salmon on bagel

That wasn’t the case, says FDA spokesman Sebastian Cianci.

“FDA is not currently conducting increased sampling for L. monocytogenes in seafood,” Cianci wrote in an email, adding that it’s possible individual seafood-processing plants or state regulators may have increased the frequency of their inspections.

Whatever the reason for the spate of recalls, repercussions have been worldwide. Undercurrent News, an industry newsletter, reported that Oslo-based Marine Harvest will close its Delifish smoked-salmon operation in Puerto Mont, Chile, this month, in part because a Listeria recall last December cost the company $4.4 million.

Delifish decided that “supplying smoked salmon from Chile for the U.S. market is not a business to be in,” an unnamed source told the online publication.

Is Smoked Salmon Safe?

Clearly, the recalls were bad for business, but what are consumers to make of this, especially given that not a single lab-confirmed case of listeriosis was linked to the recalled smoked salmon?

“Smoked fish is pretty safe, especially because it’s typically not consumed by susceptible groups or in large quantities,” said Barbara Rasco, professor in the School of Food Science at Washington State University, an expert on aquatic food and also an attorney.

Rasco thinks smoked salmon is one of the foods regulators have historically scrutinized more than others as a high risk for Listeria contamination.

But FDA wants all food products found to contain Listeria to be recalled, whether or not there has been an associated case of illness.

Since 1989, FDA has stuck to what amounts to a zero-tolerance policy for any detectable level of Listeria in food. By contrast, the European Union tolerates what it says are safe levels – anything less than 100 colony-forming units (CFU) of the bug per gram. It likely takes greater concentrations of the bacterium to constitute an infectious dose, according to Rasco.

Most people don’t get sick when exposed to Listeria, which typically causes a bout of uncomfortable diarrhea. Anyone with a healthy immune system can usually ward off any serious illness.

But if the bacteria get into the bloodstream, they can spread throughout the body and cause listeriosis, a disease Dr. Tom Frieden, director of the Centers for Disease Control and Prevention (CDC), once called “a terrible infection.” Difficult to detect or cure, listeriosis may start with a fever or stiff neck and then progress to confusion and convulsions, encephalitis and meningitis.

Nearly everyone who gets invasive listeriosis requires hospitalization and a weeks-long course of intravenous antibiotics. Odds are that the disease will kill one out of every five victims, giving it the highest mortality rate of foodborne pathogens.

That’s scary. But CDC’s latest estimates – 1,600 cases of invasive listeriosis and 260 related deaths each year – indicate that Listeria-caused illness is relatively rare in the U.S.

Still, “All these illnesses and deaths are preventable,” said Dr. Elisabeth Hagen, undersecretary for food safety at the U.S. Department of Agriculture (USDA), during a press briefing in June.

Eradication Efforts Have Stalled

Detailed rules first proposed by FDA in 2001 recommend the steps food producers should take to prevent Listeria contamination, and the agency says this processing-protocols approach to controlling the bug has worked, to a point: About 1.2 percent of ready-to-eat meat and poultry products tested positive for Listeria in 2001, compared with 0.3 percent in 2011 – a 75-percent drop, as Hagen noted in June.

Methods for testing food for Listeria have become more precise and reliable, and genetic fingerprinting developed in the 1990s has helped to identify outbreaks of listeriosis since the disease first became reportable in the 1980s.

But CDC acknowledges there’s been little headway of late in the battle to reduce cases of listeriosis.

“Rates have not budged in more than a decade,” Frieden noted at the June briefing.

Since 2008, Listeria assessment has been a priority of President Obama’s Food Safety Working Group, and, this past May, federal food regulators released a 179-page report on Listeria in ready-to-eat foods sold at retail delicatessens.

The report included storage-temperature guidelines and bacterial growth-inhibiting strategies, as well as ways to guard against contamination of incoming products and prevent cross-contamination.

Hagen unveiled the report by saying, “This assessment highlights the importance of our work to prevent Listeria from entering the retail environment in the first place, and provides a significant tool toward this effort to protect consumers and prevent foodborne illness.”

Who Gets Sick? 

Whether Listeria-contaminated food causes illness depends on the virulence and concentration of the strain, the amount eaten and the susceptibility of the consumer to infection, Rasco says.

People most at risk are those suffering from underlying health conditions, such as diabetes, or those with weakened immune systems, such as children or those undergoing cancer treatment.

People 65 and older are four times more likely than the general population to get sick from Listeria poisoning, and pregnant woman are 10 times more likely to be infected. Although a pregnant woman may not develop listeriosis herself, the pathogen can attack her fetus, resulting in miscarriage, preterm birth or stillbirth.

CDC recommends that smoked fish be avoided during pregnancy, along with hot dogs, deli meats and soft cheeses. Nevertheless, the chances are fairly remote that consuming Listeria-tainted food during pregnancy will lead to listeriosis.

Two years ago, during the outbreak of Listeria illness linked to cantaloupes, CDC confirmed 146 cases of listeriosis in 28 states. In this deadliest incidence of foodborne illness since 1924, 30 people died and one woman had a miscarriage.

CDC’s Benjamin Silk, in a video presentation about Listeria, observed: “Thousands of pregnant women consumed the Jensen Farms cantaloupe that caused the 2011 outbreak, but surveillance indicates that the attack rate of listeriosis in pregnant women was extremely low.”

Rasco thinks one reason smoked salmon doesn’t make more people sick is that the high-risk groups don’t eat it. “Kids often don’t like it, and you don’t see it served much in nursing homes or hospitals,” she said.

And, while the popularity of smoked salmon has soared, it still is considered something of a delicacy or a party food. When people consume it, they don’t eat that much of it, Rasco notes.

She says anyone concerned about the safety of smoked salmon should heat it to 145 degrees F before eating it.

Why Smoked Fish?

Listeria has cropped up in myriad raw foods, including sandwiches, leafy greens, cut celery and cantaloupe. According to USDA and FDA risk assessment, those foods at highest risk for the bacterium are soft cheeses, unpasteurized dairy (including raw milk), deli and lunch meats, smoked fish, cold cuts, hot dogs, paté and meat spreads.

Listeria lives mostly in soil, where it feeds on decaying plants, but it is also fairly ubiquitous, turning up in water, vegetation, marine sediments, sewage, animal feed and even dust. It likes damp places, such as a fish-processing plant. It will proliferate in unsanitary conditions. It can colonize drains, cooling systems and processing equipment and harbor there at length.

The bacteria multiplies in temperatures as low as 32 degrees F, so a contaminated food product that leaves the store with a relatively low load of bacteria has the potential to become deadly inside a home refrigerator. Listeria can grow at high salt concentrations, so refrigerated, cured meats and fish can harbor the pathogen.

The bug is relatively more prevalent in smoked seafood, seafood salads, luncheon meats and unpasteurized cheese, according to a study reported in the Journal of Food Protection in 2003.

That study found that 4.3 percent of the smoked seafood it tested was positive for Listeria (compared with 0.17 of the fresh soft cheese).

However, the concentration of Listeria was low in all the foods tested for this study. Only 21 of more than 31,705 food samples analyzed contained more than 100 CFU per gram. Yet, of the samples with more than 100 CFU per gram, nine were smoked seafood.

Keeping It Clean

According to FDA’s Cianci, hot-smoked fish is heated for 30 minutes at 145 degrees F, which is adequate to eliminate L. monocytogenes. But cold-smoked fish does not undergo this thermal process.

Instead, various listericidal agents approved for use in food – antibacterial sprays and rinses, ozonated water, pressure treatment, etc. – can be employed to disinfect fish that will be cold-smoked. The problems tend to crop up after the fish has been cleansed.

Care must be taken, in processing both hot-smoked and cold-smoked salmon, to avoid recontamination before the fish is packaged. A recent study of the smoked salmon industry in Scotland found that, while most processors were using appropriate food-safety practices to prepare their fish, condensation dripping from the ceiling was contaminating the finished product.

If a processor does not use a listericidal control, FDA recommends taking steps to ensure that the fish coming from a supplier is not contaminated in the first place. Insisting that suppliers provide a Certificate of Conformance or a Certificate of Analysis detailing how they sample and test their fish for Listeria would advance that goal, according to Cianci.

“Food processors should audit these suppliers on-site periodically and should test ingredients (e.g. weekly, monthly or quarterly) to verify the absence of L. monocytogenes,” Cianci added.

Essential to eliminating Listeria in commercially smoked salmon is strict adherence to Good Manufacturing Practices, FDA says. That includes designing, constructing and maintaining processing plants and equipment to minimize places where the bacteria can lodge and multiply.

The agency also recommends that smoked-fish processors write and follow a plan to test both fish samples and contact surfaces for Listeria and to address in advance what will be done if the pathogen is discovered.

© Food Safety News
  • crs

    Damned if you do, damned if you don’t. The FDA is assailed regularly for not being tough enough with inspections and recalls. But when the FDA finally shows some backbone, it’s faulted for that too!