As I mentioned in an earlier post, there’s been a large and ongoing outbreak of salmonellosis in people across the US associated with pet aquatic frogs (such as African dwarf frogs). A recent edition of Morbidity and Mortality Weekly Reports provides an update on this large and concerning outbreak. Here are the highlights regarding infections reported between April 1, 2009 and May 10, 2011.

• 224 infections with the unique outbreak strain of Salmonella Typhimurium have been identified in 42 US states. Since it is estimated that only ~3% of Salmonella infections are laboratory confirmed, this means that the number of true cases is probably much higher (e.g. >8000, if the 3% estimate is accurate).
• The median age of affected people was 5 years, with a range of <1-67 years. The young age bias may be because of increased susceptibility to infection, increased likelihood of severe infection (which would more likely result in testing) or more common exposure.
• 30% of affected individuals were hospitalized. There were no deaths.
• 65% of affected people reported contact with frogs in the week before illness. 18% of those occurred outside the home (which is why we need to make sure that even non-pet-owners are educated about zoonotic disease risks associated with pets).
• The median time from acquiring a frog to onset of disease was 15 days. This means people often got sick fairly soon after acquiring their new pet.
• One breeder in California has been implicated as a common source of infected African dwarf frogs. As with many kinds of small pets (e.g. rodents, reptiles), this is a large breeder that sells to distributors who then sell to pet stores and elsewhere. This type of mass production and distribution system means that a problem with a single breeder can result in widespread disease. This has been clearly shown previously in various other outbreaks, especially with pet rodents.

What should the average pet owner know?

• High-risk households – those including kids under the age of five, elderly individuals, pregnant women or individuals with a compromised immune system – should not have pet aquatic frogs.
• High-risk people (as describe above) should not have contact with aquatic frogs in other places.
• People with aquatic frogs should consider the frogs to be infected with Salmonella until proven otherwise. Since we don’t know how to prove otherwise, that means treat all pet aquatic frogs as infectious.
• Frog owners should avoid direct contact with the frogs and their water. Hands should be washed thoroughly after contact with frogs or their environment.
• Frog owners should never dump aquarium water into kitchen or bathroom sinks.
• Any spills of water during aquarium cleaning should be promptly and thoroughly cleaned up.
• Other pets should be kept away from aquaria (I remember when I used to have aquatic turtles and a cat. The cat used to drink from the aquarium and occasionally bat at the turtles. Not something I’d endorse now, but that was in my pre-DVM era).

This outbreak doesn’t mean that aquatic frogs can’t be good pets. It means that they shouldn’t be pets for certain people, that good routine infection control practices need to be used by frog owners and that consideration needs to be given to whether mass production of pet frogs (and other species) is appropriate.

Photo: An African dwarf frog (Hymenochirus boettgeri) (photo credit: James Gathany, CDC Public Health Image LIbrary #11831).