If people are using sacramentals thoughtlessly, or even handling things that other people will have to handle and in a way that is unsanitary, that’s a failure of prudence, and perhaps of love of neighbor.
But historically speaking, nobody has ever suggested that using sacramentals on sick people or on dirty people was sacrilegious. Indeed, most of the time people were using sacramentals and relics on sick people, because when do you really need a sacramental or a relic? So it’s not likely that would qualify. Not objectively.
Now, if you were thinking to yourself, “Mwahaha, I will infect the whole church full of people by contaminating the holy water fonts!”, obviously you’re intending sacrilege, and so then it would be objectively grave matter. Likewise, purposefully spitting or sneezing into a sacramental would count as trying to commit sacrilege.
So yeah… this is one of those things that’s not easy to classify.