A few days ago I got into a conversation with a woman I met in a store. She was using a wheelchair and told me she ALWAYS wears gloves when she leaves her own home because the ground, sidewalks, and even some public floors are likely to be full of germs. When the wheels of the chair role over them the germs are carried directly to her hands unless she's wearing gloves. Besides dirt and mud, the surfaces may have animal urine, saliva or mucus from people who spit on them, and many other unsanitary substances.
When she arrives home the gloves go directly into the dirty clothes to be washed before they're used again.
Motorized wheel chairs are less of a problem because users don't need to keep their hands on the wheels. However I would strongly suggest that anyone using the traditional type of chair have numerous pairs of washable gloves and wear some any time they go outside.