Look up camellia petal blight to find out what markers there are, like spots to indicate it is that problem in particular.

You wrote "...open flowers are brown in the very center of the bloom, and dropping of the bush...."

Sounds much like it. The camellia flower blight starts in the center of the flower or in the center of petals.

Take a sample, secured in a clear container, to a knowledgeable source, perhaps your county's Extension Service office or a large independent garden center.

We are in an ideal climate for petal blight which is caused by the fungus glomerela cingulata. It appears as brown spots and blotches over the entire flower usually in late winter-early spring.

We have noticed a similar problem starting with the center of the flower but looks different from the traditional petal blight. Could be the same thing, but I'd take the advice of jean001 and have it tested to know for sure.

I did a fair amount of looking around online before posting and couldn't quite figure out if my bloom browning/rotting had a similar pattern or not -- there is so much emphasis on the "netted" pattern of the browning of the petals, which mine don't seem to have, just brown mushiness in the very center, although maybe the disease just hadn't progressed far enough yet. Given how new it was (and the fact that it was a freebie, long story), I finally decided to just get rid of it rather than spending $$ on fungicides that might or might not help, and risking the 2 healthy established camellias I do have. I scooped up every dropped bloom, petal, leaf, and bud, as well as the leaf mulch beneath the bush and the top 1" or so of soil, and put it all -- and the plant -- in the trash can. I hope I've managed to stop the spores from becoming established in my garden....

Thanks for your help!