C.D.
The most sterile way you get a sample of urine is to catheterize (whether its an adult or an infant). Yes, it sounds horrible to do this to an infant, but the catheter is really small (much smaller than an adult size catheter). Sometimes they will do a Ubag (which is bascially a plastic bag that has an adhesive an edges that attaches to the vagina). After the baby urninates the the bag is removed. Some doctors will go directly to catheter for a sample because even with a ubag its not as accurate as a catheter (because there is bacteria everywhere and this can compromise the sample, not giving an accurate sample). If you have ever had a catheter placed in you, its very similair. I've never seen a child sedated to be catheterized. Its called a straight catheter because you are just putting in for a second to get the urine sample and then its removed right away.
With girls we really like to make sure you are wiping from front to back after diaper changes.
Uti's in infants can sometimes be a sign of possible structural defects within the bladder or ureters (the tube that connects the kidneys to the bladder). This is worst case scenario so please I'm not trying to scare you. I work in the hospital and babies are often hospitalized for uti's.