I have never replied to a forum like this, but I thought I would tell you about my five year old daughter. We have been fighting recurrent bladder infections for about 2 years. Each time she has one it is difficult to diagnose because she does not complain about pain urinating or any other sympton. I have gotten good at figuring it out because she starts having accidents and gets a little cranky and cries easily. She also give out a certain odor which I have learned to identify as a bladder infection. We did all the tests - ultrasound, dye injection into her kidneys and it all checked out okay.
About 3 weeks ago she got another bladder infection. She had been off a 3 month maintenance dose about a month when she got this. After 10 days on antiobiotics, I took her into doctor and her urine was fine. Two days later, she started acting tired, but it was holiday weekend and we were busy and traveling. She started a fever a week ago, but was eating and drinking and no other symptoms, so doctor told me to jsut watch it (I had ruled out strep throat at a minute clinic). Tonight, on teh 8th day of a fever, I noticed that the fever was gradually increasing and took her into urgent care. They told me she had a kidney infection. They said that she did not exhibit the normal signs of a kidney infection (throwing up, diarrahea, etc.). She has them so frequently but had never run a fever. Anyway, I am a little braindead at this point after being in urgent care for six hours, but I was shocked at the diagnosis. She had no symptoms except a fever and tiredness. Evidently some kids just don't show the normal symptoms. Plus, she had just finished medication for a bladder infection and her urine tested clear. It only took 2 days for her to develop a new one. They told me that since all tested okay biologically, that I should always assume with a fever that it could possibly be bladder, and we need to work on adding fiber (help with constipation), adding cranberry juice, etc.
Does this help you at all? I guess it just shows that they can happen very quickly.
Good luck!