sorry, I just read that they haven't identified the bacteria. basically, there is something causing the fever; could be viral or could be bacterial. If it is a virus, then anitbiotic will not make the sypmtoms go away and you just have to let you body fight it off. Basically, they are waiting to see if any bacteria will grow from the urine specimen and it can take a while for bacteria to show up. If he had a negative blood growth of bacteria, that is good, that means that (if there is bacteria causing the fever) it hasn't spread to the blood. Hope that helps.