Water frogs appear to be responsible for yet another Salmonella outbreak in the U.S., CDC researchers say.
A total of 85 patients in 31 states have been sickened with Salmonella typhimurium, and African dwarf frogs are the culprits.
Intermittent data on the outbreak were reported last month -- 48 infected patients in 25 states -- with a warning about proper hygiene when handling the aquatic species, if they must be handled at all. (See Another Reason Not to Kiss a Frog)
CDC researchers found that patients who'd handled a frog had nearly a 25-fold increased risk of Salmonella infection, compared with those who hadn't held an amphibian.
Reptiles have long been known to carry and transmit the bacteria. In October, the journal Pediatrics carried a report of a 2007 outbreak linked to tiny turtles -- which were banned from sale in the U.S. in the 1970s because of concerns about disease transmission. (See Little Turtles Tied to Salmonella Outbreak, Again)
There have been three multistate outbreaks of Salmonella infections associated with turtle contact since 2006, according to the CDC.
Yet this is the first reported outbreak associated with amphibians.
"Public education regarding the risk for illness associated with turtles and other reptiles should be expanded to include the risk for salmonellosis from aquatic pet frogs and other amphibians," the CDC researchers wrote.
Awareness of the outbreak began after the Utah Department of Health identified five cases of Salmonella infection between April and July 2009.
The CDC conducted a case-control study to determine the source of the infection after 11 interviews with sick patients revealed that eight reported exposure to aquatic animals.
They assessed a total of 19 cases of Salmonella and 31 matching controls from 15 states.
Cases were significantly more likely than controls to have had exposure to an aquatic pet, including fish and frogs (74% of cases versus 35% of controls).
More specifically, the illness was found to be associated with exposure to frogs (63% versus 3%, OR 24.4).
Exposure to fish was not statistically significant, and the researchers found no association between illness and consumption of any food item.
Among the 14 cases who knew what type of frog, all had exposure to an African dwarf frog.
Environmental samples from aquariums in four homes of case patients yielded Salmonella isolates matching the outbreak strain, and preliminary information has linked the frogs to the same breeder in California.
The vast majority of infected patients -- 79% -- were younger than 10.
The median age was 5, with a range of 3 weeks to 54 years, and 52% were male. No deaths were reported.
CDC researchers said the most likely source of transmission is the aquarium water, which children play with and which parents have to handle during tank cleaning.
Only about half of interviewed patients reported knowing about associations between reptile handling and Salmonella infection, and only 31% reported awareness of associations between amphibians and Salmonella.
"Although most Salmonella infections are foodborne, animal contact is an important source of human salmonellosis," the CDC researchers wrote, adding that 74,000 Salmonella infections per year are the result of reptile and amphibian exposure.