Drug-resistant Salmonella outbreak linked to ground beef

Dec 21, 2007 (CIDRAP News) – The US Department of Agriculture (USDA) yesterday issued a public health alert about ground beef products that may be contaminated with a multidrug-resistant form of Salmonella that has sickened 38 people in four western states.

The alert, issued by the USDA's Food Safety and Inspection Service (FSIS), said the illnesses are associated with multidrug-resistant Salmonella enterica serotype Newport in ground beef that may have been ground and sold at Safeway supermarkets in Arizona, California, Hawaii, Nevada, and New Mexico between Sept 19 and Nov 5.

Epidemiologic investigations and a case-control study by state health officials in Arizona and California and the US Centers for Disease Control and Prevention (CDC) found an association between fresh ground beef products and 38 illnesses that exhibited the same rare pulsed-field gel electrophoresis (PFGE) pattern in the CDC's PulseNet system. The cases include 16 from Arizona, 18 from California, 1 from Idaho, and 3 from Nevada.

The FSIS said that despite intensive, continuing investigations, it could not identify specific establishments, lots, and products that would warrant a recall.

"FSIS has no reason to believe that these products are still available for sale in commerce," the statement said, adding that people who purchased ground beef from Safeway stores on the affected dates should look for the products in their freezers and discard or destroy them.

Safeway, Inc., based in Pleasanton, Calif, said in a press release yesterday that to date, no Safeway product has tested positive for S Newport and that no illnesses have been reported in Hawaii or New Mexico, though Safeway supermarkets in those states are included in the FSIS advisory. "There is a single reported case in Idaho that has no apparent ties to Safeway stores," the company said.

However, in response to the FSIS alert, Safeway said it is asking customers who have raw ground beef products in their freezer purchased in the stores listed in the advisory between Sept 19 and Nov 5 to dispose of them.

In its advisory, the FSIS warned that in infected patients, the multidrug-resistant Salmonella strain can increase the risk of hospitalization and treatment failure.

Over the past decade, the prevalence of multidrug-resistant S Newport strains has increased dramatically in the United States. A previous study found that the most common multidrug-resistant S Newport phenotype—MDR-AmpC—increased from 1% of human S Newport isolates in 1998 to 21% of such isolates tested in 2003. The trend worries health officials, because Newport MDR-AmpC shows decreased susceptibility to ceftriaxone, the treatment of choice for invasive salmonellosis in children.

In 2002, an outbreak of Newport MDR-AmpC in ground beef sickened 47 people in five eastern states, according to previous reports. A case-control study linked the illnesses to ground beef consumption, and the pathogen was found in raw frozen ground beef from one of the patient's homes.

Studies have suggested that dairy cattle are a major reservoir for multidrug resistant S Newport. A study published in the November issue of Emerging Infectious Diseases focused on Wisconsin, a major dairy state. The researchers found that Wisconsin residents with S Newport infections during the 2003 to 2005 period were more likely to have multidrug-resistant strains, compared with the rest of the nation.

The researchers determined that patients with Newport MDR-AmpC infections were more likely than those with pansusceptible strains of S Newport to have reported contact with cattle, farms, and unpasteurized milk.

The authors wrote that intensive Newport MDR-AmpC surveillance is needed in major dairy states, and more efforts are needed to promote appropriate use of ceftiofur and other antimicrobial drugs in dairy cattle. Healthcare providers should avoid prescribing antibiotics to patients who have low-risk Salmonella infections, and public health messages should stress the importance of pasteurizing milk and cooking meat safely, the researchers said.

See also:

Dec 20 FSIS public health advisory

Dec 20 Safeway press release

Jul 2, 2002 CIDRAP News story "Drug-resistant Salmonella Newport infections linked with eating ground beef"

Karon AE, Archer JR, Sotir MJ, et al. Human multidrug-resistant Salmonella Newport infections, Wisconsin, 2003-2005. Emerg Infect Dis 2007 Nov;13(11):[Full text]

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