@bythewell - I think that adults can sometimes suffer from complications from a patent urachus that healed over when they were born, so maybe it happens more often than we think and just isn't that noticeable.
It's actually the fact that you can get thrush infections in your belly button that sounds awful to me. I know when I was a kid, I didn't really realize you had to clean the belly button very carefully and I sometimes damaged the skin there. That was sore and annoying enough, without having an actual infection in your belly button.
The only plus I can see is that it would probably be pretty localized and easy to contain. I would go straight to a doctor and apply whatever she gave me religiously until it was gone.