mw says:

I’ve cleaned various foam items over the years, and it is not simple. You need a week of hot weather so it can dry. Basically, you lay the thing outside and dowse it with soapy water, then rinse it with a garden hose. If you use soap made for furniture, or even carpet shampoo, that’s best as that kind of soap doesn’t get all sudsy. Take a bucket, fill it with warm water, pour in a half cup of carpet cleaner, then use a spritz bottle and spritz the mix all over the foam, on one side. Let it soak thru to the bottom, and sit for an hour. Then hose it thoroughly. Use up all the soapy water.
If you do this on a concrete driveway, or on a wooden porch, it works great. If you do it on grass you’ll have bits of grass all over it. After hosing it, the thing will be incredibly heavy, and needs to just sit there, draining for hours, even overnight. Once enough water has drained out, you can stand the thing on edge and lean it up against something so gravity will drain most of the rest of the water.
At some point you might try walking on it to squeeze water out. It will take days to dry, so doing this in summer, in the heat is best. Cover the thing if you get summer storms or it will absorb water again.
As for disinfecting, just use a good carpet shampoo, and the soap will kill germs.