Therapy dogs can bring more than joy and comfort to hospitalized kids. They can also bring stubborn germs.

Doctors at Johns Hopkins Hospital in Baltimore were suspicious that the dogs might pose an infection risk to patients with weakened immune systems. So they conducted some tests when Pippi, Poppy, Badger and Winnie visited 45 children getting cancer treatment.

They discovered that kids who spent more time with the dogs had a six times greater chance of coming away with superbug bacteria than kids who spent less time with the animals. But the study also found that washing the dogs before visits and using special wipes while they are in the hospital took away the risk of spreading that bacteria.

The results of the unpublished study were released Friday at a scientific meeting in San Francisco.

One U.S. health official said the findings add to the growing understanding that while interactions with pets and therapy animals can be beneficial, they can also carry risk.

“Whether covered in fur, feathers or scales, animals have the potential to carry germs that make people sick,” said Casey Barton Behravesh of the Centers for Disease Control and Prevention.

Pet therapy can help people recover from a range of health problems. Past studies have shown dogs or other animals can ease anxiety and sadness, lower blood pressure and even reduce the amount of medications some patients need.

But there have been episodes of the superbug MRSA riding around on healthy-looking therapy dogs.