They are more germ-laden than toilet seats, public restrooms, diaper-changing tables, chair armrests or playground equipment – according to University of Arizona microbiology professor Charles Gerba. He found more E. coli bacteria on shopping carts than on escalators, ATM machines, restaurants table tops and ketchup dispensers. Shopping cart contamination may contribute to winter colds and flu. Many grocery stores offer disinfectant wipes for their customers to clean shopping carts – use them.