BERN, Switzerland (AP) — Scientists now have the dirt on the rubber ducky: Those cute yellow bath-time toys are — as some parents have long suspected — a haven for nasty bugs.

Swiss and American researchers counted the microbes swimming inside the toys and say the murky liquid released when ducks were squeezed contained “potentially pathogenic bacteria” in four out of the five toys studied.

The bacteria found included legionella and pseudomonas aeruginosa, a bacterium that is “often implicated in hospital-acquired infections”.

The study by the Swiss Federal Institute of Aquatic Science and Technology, ETH Zurich and the University of Illinois was published yesterday in the journal Biofilms and Microbiomes. It’s billed as one of the first in-depth, scientific examinations of its kind.

They turned up a strikingly high volume — up to 75 million cells per square centimetre (0.15 square inch) — and variety of bacterium and fungus in the ducks.

While certain amounts of bacteria can help strengthen kids’ immune systems, they can also lead to eye, ear and intestinal infections, the researchers said.

The scientists, who received funding from the Swiss Government as part of broader research into household objects, say using higher-quality polymers to make the ducks could prevent bacterial and fungal growth.

The Swiss Government isn’t making any recommendations at this stage.

Known for their squeaks, rubber duckies have been a childhood bath-time staple for years. Online vendor Amazon.com lists one such offering — advertised as water-tight to prevent mildew — among the top 10 sellers in its “Baby Bath Toys” category.