The Centers for Disease Control and Prevention is investing an outbreak of salmonella associated with exposure to small pet turtles.

Currently, 37 cases across 13 states have been identified by the CDC, with cases ranging from March of this year to the start of August.

Sale of turtles with carapaces smaller than four inches has been prohibited in the U.S. since 1975 due to their risk of transmitting salmonella, but the CDC says "they are still available for illegal purchase through transient vendors on the street, at flea markets, and at fairs."

Six of the reported cases reported buying a turtle from a vendor or fair, or they received the turtle as a gift. Fifteen reported some exposure to a turtle's habitat prior to becoming sick. Twelve of the cases are children 5 years old or younger.

Based on genome sequencing the CDC performed on turtles collected from vendors in 2015, the strain of salmonella isolated back then is closely related to the strain isolated in patients this year. It means that the patients in this outbreak likely share a common source of infection.

Not the first time

Pet turtles exploring a habitat Turtles have been the cause for a few salmonella outbreaks. (Photo: Gustav/Shutterstock)

This isn't the first time small turtles have been responsible for a salmonella outbreak.

The black-market wildlife trade resulted in 132 reported cases of human salmonella infections across 18 states between August 2010 and September 2011. More than 60 percent of those cases were in children younger than 10. Of the 56 patients interviewed, 36 reported that they had been exposed to turtles. Fourteen of those patients identified "turtles too small to be legally traded," the CDC reported a February 2012 Morbidity and Mortality Weekly Report.

Further investigation found that the water in turtle tanks in the patients' homes tested positive for a particular strain of salmonella.

According to the report, small turtles pose a particularly high salmonella risk because they are tiny enough for children to place them in their mouths and handle them like toys.

A similar outbreak in 2007 infected 44 people in five states. A 3-week-old baby girl in Florida died in March 2007 after being exposed to her family's pet turtle.

The U.S. Food and Drug Administration also cautions against owning pet turtles, warning that salmonella can cause "diarrhea, fever, stomach pain, nausea, vomiting and headache."

The CDC offers several tips for reducing the risk [PDF] of turtle-associated salmonellosis, including thoroughly washing hands and any surfaces that turtles come into contact with. The agency recommends handling all turtles as if they could be contaminated with salmonella and warns that a negative salmonella test does not mean a turtle is not infected, as they do not "shed" the bacteria consistently. They also have a webpage devoted to keeping turtles as pets.

Editor's note: This file has been updated with new information since it was published in February 2012.