International spread of multidrug-resistant Salmonella Schwarzengrund in food products.

We compared 581 Salmonella enterica serotype Schwarzengrund isolates from persons, food, and food animals in Denmark, Thailand, and the United States by antimicrobial drug susceptibility and pulsed-field gel electrophoresis (PFGE) typing. Resistance, including resistance to nalidixic acid, was frequent among isolates from persons and chickens in Thailand, persons in the United States, and food imported from Thailand to Denmark and the United States. A total of 183 PFGE patterns were observed, and 136 (23.4%) isolates had the 3 most common patterns. Seven of 14 isolates from persons in Denmark had patterns found in persons and chicken meat in Thailand; 22 of 390 human isolates from the United States had patterns found in Denmark and Thailand. This study suggests spread of multidrug-resistant S. Schwarzengrund from chickens to persons in Thailand, and from imported Thai food products to persons in Denmark and the United States.

Multidrug-resistant Salmonella enterica serotype Typhimurium associated with pet rodents.

BACKGROUND: An estimated 1.4 million salmonella infections occur annually in the United States. The majority of these infections are foodborne, but many are acquired by contact with animals. In August 2004, isolates of Salmonella enterica serotype Typhimurium, which were indistinguishable from one another by pulsed-field gel electrophoresis (PFGE), were obtained from eight hamsters from a Minnesota pet distributor. We conducted an investigation to determine whether human cases of salmonella could be linked to this rodent-borne strain. METHODS: To identify cases of human infection with S. enterica serotype Typhimurium potentially related to pet rodents, we reviewed salmonella PFGE patterns submitted to the National Molecular Subtyping Network for Foodborne Disease Surveillance. Patients with isolates matching the hamster strain were interviewed about exposure to pet rodents. Implicated rodents were traced to pet stores, distributors, and breeders. RESULTS: We identified matching S. enterica serotype Typhimurium isolates from 28 patients in whom the onset of illness occurred between December 2003 and September 2004. Of 22 patients (or in the case of children, their parents) interviewed, 13 patients (59%) in 10 states reported exposure to pet hamsters, mice, or rats, and 2 (9%) had secondary infections. The median age of the 15 patients with primary or secondary rodent exposure was 16 years, and 6 patients (40%) were hospitalized. Thirteen associated pet stores supplied by seven distributors were identified in 10 states. No single source of the rodents was identified. The outbreak strain of S. enterica serotype Typhimurium was cultured from a patient's pet mouse and from seven hamsters from pet stores. Closely related S. enterica serotype Typhimurium isolates were cultured from rodent cages and reusable transport containers at a pet distributor. Human, rodent, and environmental isolates were resistant to ampicillin, chloramphenicol, streptomycin, sulfisoxazole, and tetracycline. CONCLUSIONS: Pet rodents probably are an underrecognized source of human salmonella infection.

Outbreak of multidrug-resistant Salmonella enterica serotype Typhimurium Definitive Type 104 infection linked to commercial ground beef, northeastern United States, 2003-2004.

BACKGROUND: Multidrug-resistant Salmonella enterica serotype Typhimurium Definitive Type 104 (DT104) emerged in the 1990s and is associated with greater clinical severity than pansusceptible S. Typhimurium. Although infection with DT104 is common in the United States, it is rarely associated with outbreaks. From October to December 2003, a cluster of DT104 infections with indistinguishable pulsed-field gel electrophoresis patterns was identified in the northeastern United States. METHODS: A case-control study that assessed exposures compared case patients to age- and geography-matched control subjects. Information on consumer purchasing and grocery store suppliers was used to trace the implicated food to its source. RESULTS: We identified 58 case patients in 9 states by pulsed-field gel electrophoresis. Representative isolates were phage type DT104 and were resistant to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline (R-type ACSSuT). Of 27 patients interviewed for the case-control study, 41% were hospitalized (median duration of hospitalization, 4 days). Compared with 71 healthy control subjects, case patients had more medical comorbidities (matched odds ratio, 4.3; 95% confidence interval, 1.5-12.7). Illness was associated with consuming store-bought ground beef prepared as hamburgers at home (matched odds ratio, 5.3; 95% confidence interval, 1.9-15.3) and with eating raw ground beef (P< or =.001). Seven case patients (27%), but no control subjects, ate raw ground beef. Product traceback linked cases to a single large ground beef manufacturer previously implicated in a multistate outbreak of highly drug-resistant Salmonella enterica Newport infections in 2002. CONCLUSIONS: This first multistate outbreak of highly drug-resistant S. Typhimurium DT104 infection associated with ground beef highlights the need for enhanced animal health surveillance and infection control, prudent use of antimicrobials for animals, improved pathogen reduction during processing, and better product tracking and consumer education.