The report published in Pediatrics on Monday found the infection sickened 376 people in 44 U.S. states and sent 29 percent of those infected to the hospital. About 70 percent of those infected were children younger than 10 years old.
The researchers linked the outbreak to an African Dwarf Frog breeding facility in Madera County, Calif. The CDC said it's not clear how the salmonella infection spread to the frogs, which transmitted it through their feces.
"This was the first Salmonella outbreak associated with aquatic frogs, and in this case the frogs are often marketed as good pets for kids," said Shauna Mettee Zarecki, the study’s lead author from the CDC in Atlanta.
"The majority of people didn’t realize there were any risks from these amphibians or other amphibians, like turtles and snakes," Zarecki added.
While most people hear about Salmonella-contaminated food, Zarecki said reptiles and amphibians also carry the bacteria. Humans can become infected after handling the animals, cleaning their containers or coming in contact with contaminated water.
People infected with Salmonella can have prolonged diarrhea, cramps, vomiting and a persistent fever. The infection can be deadly if it’s left untreated, and it’s most dangerous in the young, elderly and people with weak immune systems.
Previous research has found that reptiles and amphibians are responsible for about 74,000 Salmonella infections in the U.S. every year.
To find what was behind the outbreak, the researchers interviewed people who were infected with that strain of Salmonella from January 2008 through December 2011.
They asked each person what animals and food they were exposed to in the week before they got sick. They then compared the data from 18 people with that strain of the bacteria to 29 people who were infected with a different type of Salmonella.
Overall, they found 67 percent of the people in the outbreak were exposed to frogs during the week before their illness, compared to three percent in the comparison group.