Peanut Butter with Salmonella Affects 600 People in 47 States

04/06/07 According to the latest report from the US Centers for Disease Control and Prevention (CDC), over 600 people in 47 states are reported to have been infected from eating certain brands of peanut butter contaminated with the Tennessee strain of Salmonella since 1st August 2006.

None of the people affected by this outbreak has died.

The update to the situation is reported in today's issue of the CDC's Morbidity and Mortality Weekly Report (MMWR).

Following an investigation that begain in November 2006, Salmonella Tennessee was found to be present in jars of Peter Pan or Great Value peanut butter with a product code beginning with 2111.

The batches of peanut butter affected were made in the same factory in Georgia, belonging to food manufacturer ConAgra Foods. The manufacturer voluntarily recalled the products, destroyed any remaining batches they still had, and suspended further production while tests were carried out.

The CDC says that the incidence of reported cases of Salmonella Tennessee started tailing off shortly after the product recall in mid February this year.

Anyone who still has a jar of Peter Pan or Great Value peanut butter with a product code beginning with 2111 should throw it away immediately, said the CDC.

Public health officials started trying to track down the source of the outbreak in November 2006, when they noticed a rising trend in the incidence of Salmonella Tennessee. In 2005 and part of 2006, the incidents were occurring about one to five times a months, but in October 2006, 30 cases were reported.

On closer examination they noticed that three of the pulsed-field gel electrophoresis (PFGE) patterns of the Salmonella Tennessee strains isolated from many affected patients were closely related, suggesting a common source of contamination.

The patients did not come from the same geographical areas, and interviews conducted in November and December 2006 did not reveal any common food exposure. In January 2007 however, more patients were interviewed with a more searching questionnaire containing about 200 items. This showed that 48 per cent of patients had eaten turkey (excluding delicatessen-sliced turkey), and 85 per cent had eaten peanut butter in the week before falling ill. This was much higher than surveys of US food consumption would suggest.

The CDC then conducted a case controlled study to prove that the source of contamination was peanut butter. The study involved 65 patients over 18 years of age who had been infected with the outbreak strain of Salmonella Tennessee and had symptoms of diarrhea. They were matched with 124 randomly selected controls who were about the same age and lived in the same areas as the patients.

The study showed that patients were more likely than the controls to have eaten peanut butter (81 per cent versus 65 per cent), to have eaten it more than once a week (66 versus 40 per cent), and to have eaten either Peter Pan or Great Value peanut butter.

The CDC then informed the Food and Drug Administration (FDA), who issued a public health alert the following day, 14th February 2007.

The CDC says that new cases decreased "substantially" after that, and that investigators are trying to find out if people are still eating peanut butter from the contaminated batch.

Following the case study and the alert, the CDC and state public health laboratories then carried out tests on peanut butter jars handed in by the infected patients. They found that 21 of the jars contained a strain of Salmonella Tennessee with a PFGE pattern matching one of the outbreak strains. The jars had production dates ranging from July 2006 to December 2006.

The affected jars came from 13 states: Arkansas, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Minnesota, New York, Oklahoma, Pennsylvania, South Carolina, and Tennessee.

Officials are still unable to determine how the peanut butter became contaminated and where exactly in the plant it happened. The FDA is still investigating the plant.

There are about 2,500 strains of Salmonella that cause the infection called salmonellosis. The symptoms include diarrhea, fever, and abdominal cramps and emerge about 12 to 72 hours after exposure.

Salmonella Tennessee infection is rare, and the source is usually not known. Between 1995 and 2004, an average of 52 cases of Salmonella Tennessee were reported to the National Salmonella Surveillance System in the US each year. This represents 0.1 per cent of all reported strains of Salmonella.

According to the CDC, only one other outbreak of the strain where the food source is known has been identified. This was in contaminated milk powder.

This is the first time in the US that peanut butter has been reported as the source of a foodborne illness. There was an outbreak in Australia in 1996 of a strain of Salmonella called Mbandaka from peanut butter, and a peanut butter coated snack made in Israel was the source of an outbreak of Salmonella Agona in four other countries.

Salmonella can contaminate peanuts at any stage from when they sprout in the ground, through growth, harvesting and processing. The bacteria can withstand high temperatures, even above 70 degrees C (158 F), the temperature at which peanut butter is heat treated. The bacteria could also get into the peanut butter in the factory, from animals like rats, or from other sources, including humans not washing hands or attending thoroughly to hygiene measures.

The CDC says that even though a food production process might contain a heat treatment, this outbreak shows the need to be scrupulous about surveillance, safety and hygiene at all stages of the process.

It is estimated that every year, 76 million cases of foodborne illness occurs in the US, resulting in 325,000 hospital admissions and 5,000 deaths.