The Centers for Disease Control and Prevention (CDC) are investigating an outbreak of dozens of U.S. Salmonella cases it has linked to contact with pet turtles.

According to an advisory note posted on the CDC website Tuesday, 37 Salmonella Agbeni cases were reported in 13 states from the beginning of March this year to Aug. 3. Although no deaths have been recorded, at least 16 people have been hospitalized as a result of contracting the bacteria.

Salmonella is a bacteria that can cause a diarrheal illness that usually lasts between four and seven days. It can be especially dangerous for children, the elderly, and those with weakened immune systems.

In a factsheet titled The Trouble With Tiny Turtles the CDC advises pet owners on minimizing the risk of salmonella infection. “Don’t kiss or snuggle with your turtle,” it warns, while suggesting turtle owners wash their hands after touching their pets.

Read More: Why You Really Shouldn’t Hug Chickens

Although turtles of any size can carry Salmonella, tiny turtles are especially risky. Since 1975, the FDA has banned selling and distributing turtles with shells less than 4 inches long as pets because they are often linked to Salmonella infections.

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Write to Joseph Hincks at joseph.hincks@time.com.