High contact areas are among the germiest places in hotel rooms, according to a study presented at the American Society for Microbiology.

Researchers swabbed 18 surfaces in three hotel rooms to check for levels of bacterial contamination. Within the rooms, high contact areas like TV remotes, telephones, and light switches had the highest levels of bacteria contamination, while headboards and bathroom door handles had the lowest levels.

Items in housekeeper’s carts, such a mop heads and sponges, were also quite contaminated. This could lead to cross-contamination between rooms.

Researchers say that high levels of bacterial contamination indicate that the rooms were not that clean. They couldn’t say that bacterial contamination in the hotel rooms would cause disease, but they acknowledge that unclean rooms could be risky for people with weakened immune systems.

Knowing which surfaces have the highest levels of contamination would allow housekeeping managers to prioritize cleaning time to reduce bacterial contamination in hotel rooms, says Katie Kirsch, the main presenter. The authors note that there are no industry-wide standards for room cleaning and that the current method of assessing room cleanliness-visual inspection-is ineffective.

They call for industry-wide standards for cleaning hotel rooms.