That's simply not true at all.
Natural penises are not difficult to clean in the least, in fact, it's quite pleasurable to do so. I've never heard of a single infection that anyone has caught because of being natural. The body is very well equipped to deal with that kind of thing in such a sensitive area.
It's also no more hygienic to be circumcised. The build up that occurs under the foreskin isn't dirt at all - it's called smegma, and it's a natural anti-bacterial agent that actually helps protect the penis.
From all of the information I've read, there is really no benefit to being natural or circumcised. It makes little difference.