Investigation Update: Outbreak of Human Salmonella Typhimurium Infections Associated with African Dwarf Frogs

April 28, 2011

Introduction

The Centers for Disease Control and Prevention (CDC) is collaborating with public health officials in many states to investigate a multistate outbreak of human Salmonella Typhimurium infections associated with African dwarf frogs, a type of water frog. African dwarf frogs commonly live in habitats containing water such as aquariums or fish tanks.

As of April 21, 2011, a total of 218 individuals infected with the outbreak strain of Salmonella Typhimurium have been reported from 41 states since April 1, 2009. The number of ill person identified in each state is as follows: Alaska (5), Alabama (2), Arizona (10), California (18), Colorado (12), Connecticut (3), Florida (1), Georgia (4), Idaho (4), Illinois (8), Indiana (1), Kansas (2), Kentucky (4), Louisiana (2), Massachusetts (6), Maryland (5), Michigan (6), Minnesota (1), Missouri (5), Mississippi (1), Montana (2), North Carolina (1), Nebraska (2), New Hampshire (3), New Jersey (3), New Mexico (2), Nevada (3), New York (7), Ohio (7), Oklahoma (1), Oregon (5), Pennsylvania (15), South Dakota (3), Tennessee (4), Texas (4), Utah (18), Virginia (11), Vermont (1), Washington (22), Wisconsin (3), and West Virginia (1).

Among persons for whom information is available, illnesses began April 9, 2009. Infected individuals range in age from less than 1 year old to 67 years old. Seventy-one percent of patients are younger than 10 years, and the median age is 5 years. Fifty-one percent of patients are female. Among ill persons, 30% were hospitalized. No deaths have been reported.

The outbreak can be visually described with a chart showing the number of people who became ill each day. This chart is called an epi curve. Illnesses that occurred after March 25, 2011, might not be reported yet due to the time it takes between when a person becomes ill and when the illness is reported. This takes an average of 2 to 3 weeks. Please see the Timeline for Reporting of Salmonella Cases for more details.

Surveillance for additional illnesses is continuing through PulseNet, the national network of public health and food regulatory agency laboratories coordinated by CDC. During 2010, a retrospective review was conducted of cases reported to PulseNet in 2008. Twenty-five of 116 persons with illnesses between April 2008 and March 2009 were interviewed. Seventy-nine percent (19/24) reported exposure to water pets, and 60% (15/25) reported exposure to frogs.  Of those who knew the type of frog, 71% (5/7) identified African dwarf frogs.  These data suggest this outbreak may have been ongoing since April 2008.

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Investigation of the Outbreak

CDC, in collaboration with many state and local health departments, is continuing to investigate an outbreak of Salmonella Typhimurium infections associated with African dwarf frogs, a type of water frog, and water from their habitats (e.g., aquarium or fish tank). In interviews, ill persons answered questions about contact with animals and foods consumed during the week before becoming ill. Sixty-five percent (56/86) of ill persons interviewed reported contact with frogs in the week before their illness began. Of ill persons who could recall the type of frog they had contact with, 85% (29/34) identified African dwarf frogs. The median time from acquiring a frog and illness onset was 15 days, with a range of 7 to 240 days.

Findings of multiple traceback investigations of African dwarf frogs from homes of ill persons have identified a single African dwarf frog breeder in California as the source of these frogs. This frog breeding facility was first identified as the source of African dwarf frogs associated with human infections in 2010. Environmental samples taken at this breeding facility in January and April 2010 and tested in CDC laboratories yielded isolates of Salmonella Typhimurium matching the outbreak strain. Additional information about this investigation in 2009-2010 can be found on the CDC Salmonella page.

In 2009, samples taken from aquariums containing aquatic frogs in four homes of ill persons yielded the outbreak strain. Environmental samples from two African dwarf frog distributors who obtain their frogs from the California breeder yielded the outbreak strain.  In March 2011, testing conducted by the New York State Department of Health Wadsworth Center Laboratory of a water sample collected from an aquarium containing African dwarf frogs in the household of a sick infant also identified the outbreak strain. In April 2011, testing conducted by the Michigan Department of Community Health from a swab of an African dwarf frog and a water sample and rocks collected from the frog's aquarium—all from the household of a sick child—identified Salmonella Typhimurium; additional testing is ongoing to determine if this Salmonella isolate is the outbreak strain.

Because of the evidence of an ongoing problem, local health department officials visited the frog breeder again in late March 2011 and collected additional environmental samples. These samples were tested in CDC laboratories and most yielded isolates matching the outbreak strain of Salmonella Typhimurium. Additional environmental samples obtained from the frog breeder facility were tested by the California Department of Public Health Microbial Diseases Laboratory Branch, and most samples yielded isolates matching the outbreak strain.

Epidemiologic, traceback, and laboratory findings between 2009 and 2011 link this ongoing outbreak of human Salmonella Typhimurium infections to a single African dwarf frog breeding facility in California.

On April 19, 2011, the owner of the frog breeding facility voluntarily stopped shipping African dwarf frogs and has been cooperating with public health officials. African dwarf frogs from this frog breeding facility were not sold directly to pet stores or to the public.  However, it is possible that African dwarf frogs distributed before April 19th are still in stores and homes. The California Department of Public Health sent a letter to the direct customers of the breeder to recommend they discontinue distribution and sale of these frogs and decontaminate the tanks or aquariums in which they were kept.

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Clinical Features/Signs and Symptoms

Most persons infected with Salmonella bacteria develop diarrhea, fever, and abdominal cramps 12 to 72 hours after infection. The illness usually lasts 4 to 7 days, and most persons recover without treatment. However, in some persons, the diarrhea may be so severe that the patient needs to be hospitalized. Salmonella infection may spread from the intestines to the bloodstream, and then to other body sites and can cause death unless the person is treated promptly with antibiotics. The elderly, infants, and those with impaired immune systems are more likely to have a severe illness from Salmonella infection. More general information about Salmonella can be found here.

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Advice About How to Prevent Infections from African Dwarf Frogs and Other Types of Water Frogs

• Wash hands thoroughly with soap and water right after handling anything, including water, that comes in contact with water frogs or from inside their habitat (e.g., aquarium or fish tank). Since the water from inside their habitat can carry the same germs as the water frogs themselves, following proper hand washing practices is very important. Adults should assist young children with hand washing.
• Kitchen sinks should not be used to empty or wash the frog’s habitat (e.g., aquarium or fish tank). If possible, empty and wash the habitat outside of the home, using disposable gloves. If bathtubs are used for cleaning the frog’s habitat, they should be cleaned thoroughly and disinfected with bleach. Young children should not be allowed to clean the frog’s habitat.
• Be aware that Salmonella infections can be caused not only by water frogs, but by other amphibians and reptiles, such as turtles. More information about how to enjoy pets safely can be found on the CDC Healthy Pets Healthy People Website.

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Advice to Parents and Caregivers

• People at highest risk for serious Salmonella infections are children under 5 years old, older persons, pregnant women, or people who have weak immune systems, such as cancer patients and those undergoing chemotherapy or organ transplants. These people should avoid contact with water frogs and anything that comes in contact with these frogs, their water, and their habitat (e.g., aquarium or fish tank).
• Water frogs are not an appropriate pet for children under 5 years old, and if possible, should not be present in homes with children of this young age. Also, keep water frogs out of childcare centers, hospitals, and nursing homes.
• Keep any habitat with water frogs out a child’s bedroom, especially children under 5 years old. Handle all surfaces that have come in contact with water frogs as if they are contaminated with Salmonella bacteria, because there is a good possibility that they are.
• If you have a water frog, watch for symptoms of Salmonella infection, such as diarrhea, fever, and abdominal cramps. Call your health care provider if you or a family member develops these symptoms.

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Advice to Pet Stores/Others Who Sell or Display Water Frogs

• Pet stores and others who sell water frogs should not continue to sell African dwarf frogs from the implicated frog breeding facility. Check with your distributors to determine if you have received African dwarf frogs from this facility.
• Pet stores and others who sell or display water frogs should provide health-related information to owners and potential purchasers of water frogs near the water frog display prior to the point of purchase, not at the cash register. This should include information about the risk of acquiring a Salmonella infection from water frogs and water in their habitat (e.g., fish tank or aquarium) and instructions for proper cleaning of the frog’s habitat.
• More information on displaying animals in public settings can be found in the 2009 Compendium of Measures to Prevent Diseases Associated with Animals in Public Settings.

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Advice to Health Care Providers

• Ask parents or caregivers about pet and animal ownership, especially amphibians (e.g., frogs) and reptiles (e.g., turtles), and provide education about the risk of acquiring a Salmonella infection from contact with the animals, their habitat (e.g., fish tank or aquarium), or water. Advise parents and caregivers on proper handwashing practices.

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Advice to Veterinarians

• Provide education to clients with water frogs about the risk of acquiring a Salmonella infection from contact with water frogs and water from their habitat (e.g., fish tank or aquarium).
• Provide education to clients with water frogs on how to properly clean the water frogs’ habitat.

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