The Centers for Disease Control and Prevention announced an investigation Tuesday into an ongoing outbreak of a rare subtype of Salmonella enterica linked to exposure to pet turtles.

So far, the outbreak involves 37 cases of Salmonella enterica serovar Agbenia infections across 13 states, which led to 16 people being hospitalized. Overall, 12 of the sickened people are children aged five or younger, an age group particularly vulnerable to the bacteria. No deaths have been reported.

With lab testing and epidemiological data, the CDC linked the outbreak to exposure to pet turtles or their habitats. The charmingly slow, half-shelled reptiles are known carriers of Salmonella. When infections jump to humans, they can cause diarrhea, fever, stomach pain, nausea, vomiting, headache, and urinary tract infections. Young children, the elderly, and those with compromised immune systems are particularly vulnerable. For these reasons, the CDC has warned of the dangers of owning pet turtles, particularly tiny ones that children like to handle, snuggle, and—in some cases—pop into their mouths.

In 1975, the Food and Drug Administration banned the sale of turtles with a shell less than four inches long. The CDC estimates that the ban averts 100,000 cases of Salmonella infections—salmonellosis—each year in US children.

Turtle power

But all turtles risk shedding Salmonella, which they naturally carry without showing any symptoms or signs of carriage. Even turtles that have tested negative in the past may still possess the bacteria and spread it later. The CDC estimates that turtles and other reptiles cause 74,000 cases of salmonellosis each year in the US.

Between January 2015 and April 2016, there were four outbreaks of salmonellosis in the US linked to pet turtles, sickening 133 in 26 states. There were no deaths in those outbreaks, but that’s not always the case. For instance, in 2007, a four-week-old baby in Florida died of salmonellosis directly linked to a small turtle.

The Salmonella subtype linked in this case is the rare Salmonella Agbenia. It was isolated in the 1950s from the stool sample of a Nigerian child named Agbenia, who was suffering from diarrhea. Since then it has popped up sparingly in case reports and outbreaks around the world. Notably, in June of 2011, it caused a small eight-person outbreak, mostly among guests at a wedding. No specific source of the infection was ever identified and food at the wedding was ruled out. Prior to that, there had only been eight cases in the whole of Canada between 2000 and 2010.

To avoid catching such an infection from a pet turtle or other reptile, health experts say to remember that they’re cute but contaminated. Experts suggest washing hands and surfaces promptly after playing with a turtle and keeping them away from high-risk individuals, such as young kids or those with compromised immune systems.

“Even if a small turtle doesn’t look sick, it may still carry Salmonella that could make young children sick. And unfortunately, children will unknowingly infect themselves,” Vic Boddie II, a consumer safety officer in the FDA’s Center for Veterinary Medicine, said in a safety announcement. “Kids have the tendency to put the small turtles in their mouths or play in the turtle habitat and then put their fingers in their mouths. Also, reptile habitats are sometimes cleaned in the kitchen sink, which could cross-contaminate food and eating utensils, thus posing a serious risk to both kids and the elderly.”

The bacteria can survive for a long time on contaminated surfaces, the FDA warns, so cleaning up afterward is “extremely important.”