Would you like a side of poop with your McGriddle? If you use the touchscreen monitors at McDonald’s to order it, you might not have much of a choice. In a recent investigation by the UK newspaper Metro in collaboration with London Metropolitan University, researchers found fecal matter on every touchscreen they tested across eight different McDonald's restaurants.

They swabbed the surfaces of touchscreen devices that had recently been rolled out at eight McDonald’s locations in the UK (six in London and two in Birmingham). All of them contained coliforms, which are bacteria found in digestive tracts and feces. A sample from one of the screens also tested positive for Staphylococcus aureus, a bacteria that can cause skin infections, food poisoning, and occasionally more serious conditions like blood poisoning and toxic shock syndrome. Listeria and Proteus bacteria, which can also pose health threats, were detected on touchscreens in a few restaurants as well.

Paul Matewele, a microbiology lecturer at London Metropolitan University, said he was shocked to see such a high prevalence of gut and fecal bacteria on the touchscreens. Their use in fast food establishments is becoming increasingly common, but as this analysis shows, they do come with risks.

“Touchscreen technology is being used more and more in our daily lives but these results show people should not eat food straight after touching them. They are unhygienic and can spread disease,” Matewele told Metro. “Someone can be very careful about their own hygiene throughout the day but it could all be undone by using a touchscreen machine once.”

A McDonald’s spokesman said that the restaurants clean their self-order screens often throughout the day, but Matewele said the disinfectant must not be strong enough to kill all of the bacteria. However, as Newsweek notes, the sample size for the study was quite small. It only tested touchscreens at eight out of roughly 1300 McDonald's restaurants in the UK.

The more something is touched by multiple people, the more likely it is to harbor harmful germs. Beyond fast food joints, bacterial hotbeds include elevator buttons, office doors, and airport security bins. If you're going to be touching any of these surfaces, just be sure to wash your hands before eating. Big Macs included.

[h/t Metro]