Salmonella cases linked to pet rodents

May 6, 2005 (CIDRAP News) Fifteen cases of multidrug-resistant Salmonella infection have been traced to contact with hamsters, mice, and rats, marking the first human salmonellosis outbreak linked to pet rodents, the Centers for Disease Control and Prevention (CDC) announced yesterday.

The investigation connecting human and rodent cases involving Salmonella enterica serotype Typhimurium began last summer, after a 4-year-old South Carolina boy and a 5-year-old Minnesota boy fell ill. One had just bought a hamster, the other a mouse. Both rodents died within a week after the sale, according to an article published in today's issue of Morbidity and Mortality Weekly Report (MMWR).

A joint CDC and Minnesota Department of Health (MDH) investigation that included a review of isolates submitted to the PulseNet National Salmonella Database in 2004 showed 28 matching human case-isolates from 19 states. Of 22 patients interviewed, 13 (59%) had had contact with rodents from pet stores. Two patients (9%) became ill through secondary exposure. Seven of the 22 patients (32%) had no known rodent contact. Four people remained under investigation and two were lost to follow-up, the CDC reports.

The patients with known primary or secondary rodent exposure came from 10 states. Symptoms included abdominal cramps, fever, vomiting, and bloody diarrhea. Six patients had been hospitalized, but none died. Both human and animal S Typhimurium isolates were uniformly resistant to ampicillin, chloramphenicol, streptomycin, sulfizoxazole, and tetracycline.

Hamsters involved in the investigation were found to be part of a shipment of 780 hamsters received in Minnesota on Aug 1, 2004, from an Iowa pet distributor, the CDC reports. Of those hamsters, 243 were sent to 15 retail pet stores in four midwestern states. Shipments stopped on Aug 23 after many hamster deaths. By the end of August, 320 of the remaining 537 hamsters at the Minnesota distributor had died, most after bouts of diarrhea. The remaining hamsters were euthanized.

Tracing of rodents from exposed patients led to pet distributors in Georgia, Arkansas, and Iowa, but no common link among the three main distributors was found, the article says. Systematic environmental cultures were taken only at the Georgia site, where S Typhimurium was found in rodent cages, rat bins, and mice and rat pellets. In addition, several rodent breeders/distributors said they routinely gave antimicrobials to rodents at several points in the raising and distribution process.

"One pet distributor used rodent feed containing tetracycline for all rodent feedings," the article states. The preventive use of antibiotics might have facilitated the spread of multidrug-resistant Salmonella in the "pocket pet" industry, the CDC says. "This use might have contributed to disease in colonized animals and increased shedding of Salmonella, thus facilitating increased transmission among animals and from animals to their human caretakers."

The CDC says healthcare workers should consider pet rodents a possible source of Salmonella and obtain cultures when investigating outbreaks. The agency also suggests improving hygiene in rodent cages and reducing unnecessary antimicrobial use.

The CDC recently released a fact sheet that provides tips on buying pocket pets and minimizing the risk of salmonellosis associated with them. It says that thorough handwashing after handling rodents or their cages and bedding is the most important preventive step. The agency also says young children should be kept away from rodent waste.

CDC. Outbreak of multidrug-resistant Salmonella Typhimurium associated with rodents purchased at retail pet storesUnited States, December 2003October 2004. MMWR 2005 May 6;54(17):429-33 [Full text]