Notes from the Field: Update on Human Salmonella Typhimurium Infections Associated with Aquatic Frogs --- United States, 2009--2011

CDC is collaborating with state and local public health departments in an ongoing investigation of human Salmonella Typhimurium infections associated with African dwarf frogs (ADFs) (1). ADFs are aquatic frogs of the genus Hymenochirus commonly kept in home aquariums as pets. From April 1, 2009 to May 10, 2011, a total of 224 human infections with a unique strain of S. Typhimurium were reported from 42 states. The isolates are indistinguishable by pulsed-field gel electrophoresis and multiple-locus variable-number tandem repeat analysis. This outbreak likely includes considerably more than the 224 laboratory-confirmed cases reported to CDC; only an estimated 3% of Salmonella infections are laboratory confirmed and reported to surveillance systems (2). Surveillance for additional cases continues through PulseNet, the national molecular subtyping network for foodborne disease surveillance.

The median age of patients in this outbreak was 5 years (range: <1--67 years), and 70% (156 of 223) were aged <10 years. Approximately 52% (111 of 215) were female. No deaths have been reported, but 30% (37 of 123) of patients were hospitalized. Sixty-five percent (56 of 86) of patients interviewed reported contact with frogs in the week before illness; 82% (45 of 55) reported that this contact took place in the home. Of those who could recall the type of frog, 85% (29 of 34) identified ADFs. Median time from acquiring a frog to illness onset was 15 days (range: 7--240 days).

Samples collected during 2009--2011 from aquariums housing ADFs in six homes of patients yielded the S. Typhimurium outbreak strain. Traceback investigations conducted during 2009--2011 from 21 patient homes and two ADF distributors identified a breeder in California as the common source of ADFs. This breeder sells ADFs to distributors, not directly to pet stores or to the public. Environmental samples collected at the breeding facility in January 2010, April 2010, and March 2011 yielded the outbreak strain. Based on these epidemiologic, traceback, and laboratory findings, the breeder voluntarily suspended distribution of ADFs on April 19, 2011. Public health officials are working with the breeder to implement control measures.

Distribution of ADFs currently is unregulated by federal or state agencies. To prevent infection, the public needs to be aware of the risk of Salmonella infections associated with keeping amphibians, including frogs, as pets. Education of consumers, health-care professionals, and the pet industry is needed. Persons at high-risk for Salmonella infections, especially children <5 years, pregnant women, and immunocompromised persons, should avoid contact with frogs, water used by the frogs, and their habitats. Additional information is available at http://www.cdc.gov/salmonella/water-frogs-0411.

Reported by

Jill Yaeger, Phil Hudecek, Madera County Dept of Environmental Health. Curtis L. Fritz, Debra Gilliss, Duc J. Vugia, Gregory Inami, Rita A. Brenden, California Dept of Public Health. Jennifer K. Adams, Cheryl A. Bopp, Eija Trees, Vincent Hill, Amy Kahler, Jeshua Pringle, Ian Williams, Casey Barton Behravesh, Div of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases; Sarah D. Bennett, Shauna L. Mettee, EIS officers, CDC. Corresponding contributor: Sarah D. Bennett, sbennett@cdc.gov, 404-639-2274.

References

1. Multistate outbreak of human Salmonella Typhimurium infections associated with aquatic frogs---United States, 2009. MMWR 2010;58:1433--6.
2. FoodNet estimate of the burden of illness caused by nontyphoidal Salmonella infections in the United States. Clin Infect Dis 2004;38:S127--34.