Nineteen people in seven states have now been confirmed infected with a multi-drug resistant strain of Salmonella Typhimurium in the outbreak linked to contaminated ground beef sold at Hannaford Supermarkets, the Centers for Disease Control and Prevention reported Thursday.

That’s three more cases of Salmonella infection confirmed since the CDC’s last report on the outbreak, Dec. 20, 2011. The new cases were reported in New Hampshire and New York.

Hannaford Supermarkets, a chain based in Scarborough, ME, recalled an undisclosed amount of fresh ground beef on Dec. 15. There’s still no official word on who supplied the beef to Hannaford, but Cargill Inc. says it was contacted this week as part of a routine traceback of all Hannaford suppliers. Cargill said it has found no evidence its beef was contaminated.

The outbreak investigation has been unable to determine the source of the beef because of Hannaford’s inadequate records and grinding practices, according to the USDA.

In its latest outbreak report, the CDC said testing by the Maine Health and Environmental Lab and the New York Department of Health, Wadsworth Center Laboratories isolated the outbreak strain of Salmonella Typhimurium from different samples of leftover ground beef purchased from Hannaford stores and collected from two unrelated outbreak victims’ homes in Maine and New York.

Epidemiologic evidence led outbreak investigators to Hannaford’s ground beef. Among 18 of the ill people, 14 – or 78 percent – recalled eating ground beef during the week before they got sick. By comparison, only 40 percent of a control group of healthy individuals reported eating ground beef during the prior week. 

Among 14 of the ill people who had eaten ground beef, 12 – or 86 percent – said they had purchased the meat from Hannaford stores between Oct. 12 and Dec. 10, 2011. 

The outbreak has sent at least seven people to the hospital, according to the CDC. They are infected with a strain of Salmonella that is resistant to several commonly prescribed antibiotics. Antimicrobial resistance not only can increase the risk of hospitalization, it also increases the risk that treatment will fail for those infected with Salmonella.

The CDC said isolates collected from five of the case patients indicated the outbreak bacteria are resistant to amoxicillin/clavulanic acid, ampicillin, ceftriaxone, cefoxitin, kanamycin, streptomycin and sulfisoxazole; and some are also resistant to tetracycline. The isolates are sensitive to several common antibiotics used in clinical practice such as ciprofloxacin, gentamicin and trimethoprim-sulfamethoxazole, the CDC added.

New Hampshire has reported six cases associated with the outbreak, New York five and Maine four, while Hawaii, Kentucky, Massachusetts and Vermont each have reported one case.

The ill people range in age from 1 to 79; the median age is 44. 

Once again, the CDC warned that the recalled ground beef, which was sold fresh with a sell-by date of Dec. 17, could still be in freezers. It should not be eaten, the CDC advised.

CDC Outbreak Map: