May 31, 2007 (CIDRAP News) – The US Centers for Disease Control and Prevention (CDC) today released a detailed report on the recent nationwide Salmonella outbreak linked to certain peanut butter brands, showing the number of sick patients has grown by nearly 200 since the agency's last update in March.
The report, published in the Jun 1 issue of Morbidity and Mortality Weekly Report (MMWR), said as of May 22, 628 people from 47 states were sickened by one of the three Salmonella enterica serovar Tennessee strains that were linked to the outbreak by PulseNet, an electronic network for sharing molecular fingerprinting (pulsed-field gel electrophoresis) data about foodborne pathogens.
The source of the peanut butter contamination is still not known, the CDC report said. "Local and state public health officials in multiple states, with assistance from the CDC and the Food and Drug Administration (FDA), are continuing to investigate this outbreak caused by peanut butter, a new food source for salmonellosis in the United States," the CDC report said.
In early April, ConAgra, the producer of the implicated peanut butter, blamed the contamination on moisture from a roof leak or faulty sprinkler system that could have triggered bacterial growth at the Sylvester, Ga., plant where the peanut butter was produced. The FDA, however, has not yet released a report on its findings at the plant.
The CDC report said investigators isolated two environmental samples of the outbreak strain from the plant, along with 21 from opened and unopened jars of two peanut butter brands that were the subject of the recall: Peter Pan and Great Value with a product code beginning with 2111.
The Salmonella outbreak investigation began in November 2006 when PulseNet officials first noticed a substantial increase in the number of S enterica serovar Tennessee cases, according to the MMWR report. During the previous year, the network typically recorded 1 to 5 cases per month, but in October, the number swelled to 30. Three closely related genetic patterns were associated with the outbreak.
Initial patient interviews in late 2006 found that 85% of patients had eaten peanut butter the week before they got sick, which the CDC said was higher than expected for the US population. A case-control study, which included 65 patients and 124 controls, was conducted in early February and revealed that the sick patients were more likely to have eaten peanut butter and to have eaten either Peter Pan or Great Value brands.
Peanut butter made at the plant was exported to 70 other countries. No confirmed cases have been linked to the outbreak, though several possibly related cases have been investigated, the CDC reported.
The ages of the affected patients ranged from 2 months to 95 years, and 73% were female, the report said. The most common symptoms were diarrhea, abdominal cramps, dysuria, and fever. Twenty percent of patients were hospitalized, and no deaths were reported.
Illness onset dates, known for 481 of 628 patients, ranged from Aug 1, 2006, to Apr 23, 2007. The CDC said reports of new cases dropped sharply after Feb 14 when the FDA issued a health alert about contaminated peanut butter and the company recalled the products.
In an editorial note that accompanied the MMWR report, the CDC noted that infections involving S enterica serovar Tennessee are rare, representing 0.1% of all reported Salmonella strains. The only other food-related outbreak in the United States that involved the strain was linked to contaminated powdered milk products and infant formula in 1993, the CDC report said.
The outbreak strain is one of the Salmonella subtypes that are more likely to cause urinary tract infections (UTIs), and because such UTIs are more common in woman, the high number of isolates from urine (35%) in this outbreak may explain the high number of cases in females (73%), the CDC noted.
The CDC said the Salmonella outbreak was the first-ever foodborne illness traced to peanut butter in the United States; however, it noted that other countries have reported contamination of peanut butter or products that contain peanut butter by two other S enterica serotypes.
Peanuts can become contaminated with Salmonella during growth, harvest, or storage, and the organisms can survive in a high-fat, low-water environment, despite heat treatment that typically exceeds 158°F, the report said. Contamination can also occur after production from various sources, including raw peanuts, animals, humans, or other food ingredients, the CDC noted.
"This outbreak demonstrates the potential for widespread illness from a broadly distributed contaminated product," the editorial said, adding that the outbreak serves as a reminder that contamination can occur, even in products that are processed with heat, and that effective controls to prevent contamination are needed in food-processing plants.
Some consumers may still be eating the contaminated peanut butter, and the CDC said that all remaining jars of Peter Pan and Great Value peanut butter subject to the recall should be discarded.
CDC. Multistate outbreak of Salmonella serotype Tennessee infections associated with peanut butter—United States, 2006-2007. MMWR 2007 Jun 1;56(21):521-4
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