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Lethal Listeria Outbreak Tied to Hog Head Cheese

Food Safety News

By Mary Rothschild | April 08, 2011

In August, 2010, a half million pounds of sausages and hog head cheese were pulled off Louisiana grocery shelves in a recall triggered by what the state Department of Agriculture and Forestry said were Listeria monocytogenes isolates detected in a product sample from Veron Foods.

The contamination was discovered in the Prairieville-based company's products, according to the news release, "through a foodborne illness investigation."

There was no indication of whether that meant one illness or multiple illnesses.

Less widely circulated than the recall notice, however, was the Louisiana Morbidity Report, September-October 2010, which on page 5 revealed that behind the recall was a significant foodborne illness outbreak -- 14 cases of listeriosis.

The Louisiana Listeria outbreak is now disclosed in detail by the Centers for Disease Control and Prevention in its most recent Morbidity and Mortality Weekly Report, issued Thursday. The case, according to the CDC, was the first published report of an invasive listeriosis outbreak associated with hog head cheese.

The CDC report also mentions something else the Louisiana report did not: Seven of the 14 listeriosis cases were so severe the individuals had to be hospitalized. And two of the case patients died.

The CDC says it wasn't surprising that an outbreak involving hog head cheese occurred. Hog head cheese is not actually cheese, but a sort of meat aspic made from pig heads and feet and usually served as a cold cut or appetizer. Like any ready-to-eat deli meat, it can pose a risk, especially to older adults, pregnant woman and people with chronic health problems.

What is unusual is that the illnesses weren't widely publicized. When contaminated food is removed from the market, health authorities usually disclose whether it is making people sick.

The CDC says that from January to June, 2010, 14 lab-confirmed cases of listeriosis were reported to the Louisiana Office of Public Health, a high number for a department that typically sees an average of 5 listeriosis cases over the same time span.

The cases were uploaded to PulseNet, the nationwide laboratory system based at the CDC in Atlanta. PulseNet helps epidemiologists connect seemingly unrelated cases of foodborne illness, and recognize outbreaks much faster.

Louisiana's report says that helped determine the Listeria illnesses were probably related to a common food source: "Without the PulseNet program and the participation of hospital laboratories in sending bacteria isolates to the State Public Health Laboratory this cluster may have gone undetected and potentially more people would have become ill."

The subsequent epidemiologic investigation focused in particular on four patients: two who reported eating hog head cheese from the same grocery store, another who remembered eating it at another grocery store in a different city and a fourth who simply recalled eating deli meats. The traceback investigation found that the grocery stores sold only one brand of hog head cheese, the clue that it was the likely outbreak source.

Unopened packages of head cheese were collected and the outbreak strain was isolated from a sample of the spicy hog head cheese variety. Later, at the processing plant, Listeria matching the outbreak strain was found in a refrigeration unit and on a door threshold.

At some point during this time, the recall alert was issued for all packages of Veron's hot smoked sausage, mild smoked sausage, andouille sausage and hog head cheese. The other products were included in the recall, the report said, because all had been processed using the same equipment.

Veron is not mentioned by name in the CDC report. It is described as a "small, state-inspected processing establishment ... which produces approximately 600 pounds of hog head cheese per week."

The CDC says the plant was under federal inspection until January 2007. Prior to that, routine testing by the U.S. Department of Agriculture's Food Safety and Inspection Service (FSIS) had detected L. monocytogenes contamination in October and December 2006, which led to a voluntary recall of 290 pounds of hog head cheese in January 2007.

But the four L. monocytogenes isolates from the samples FSIS had collected in 2006 did not match the 2010 outbreak-related strain. In addition, Listeria contamination was not detected in any of the 12 product samples Louisiana state inspectors had collected at the plant since 2007.

However, because the outbreak strain was identified at the plant several weeks after the implicated head cheese had been processed, CDC officials said that indicated "persistent environmental contamination in the processing establishment was responsible for product contamination and resulting illnesses."

Listeria is a particularly nasty pathogen, which can survive under refrigeration and is known to harbor in places such as drains, on conveyor belts, in air filters and ice makers for months and even years.

In the United States, it is estimated to cause 1,591 illnesses and 255 fatalities a year. Neonatal infections are the most severe, with mortality rates as high as 50 percent.

In 2010, among other outbreaks of listeriosis, seven people became ill in Texas in an outbreak linked to chopped celery and two Oregon mothers and their prematurely born infants, as well as a pregnant woman in Washington state, were sickened in an outbreak traced to fresh cheese.

One of the worst recent outbreaks of listeriosis occurred in 2008 in Canada, when contaminated deli meats caused 57 illnesses and 22 deaths and led to a massive recall of 220 products.

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