Hello and thank you for your question. Congratulations on 14 years post kidney transplant - I hope your kidney continues to do well for you. Most UTI s are not caused by sexual activity. They are caused by germs (bacteria) that are present on the skin that travel back up the urethra to the bladder, and from there, sometimes to the kidneys. Urinary infections in women do often occur after intercourse, just because intercourse can irritate the skin around the urethra, but any irritation of the skin can make infection more likely, and the usual germs that cause infection are bacteria from our gastrointestinal tract. Infants and young children often develop urinary tract infections because of diapers and issues learning to wipe adequately. Urinary infections can occur in healthy males and females at any age with no identifiable predisposing cause. Anything that decreases the immune system (such as taking medicine to prevent rejection of a kidney) can make a person more likely to develop a urinary tract infection. And ciprofloxacin has been my hands-down favorite antibiotic for urinary tract infection when I want to use something strong. This is the antibiotic for someone who has a kidney transplant, or history of kidney infections when they get UTI, or over 65, or other reasons we go for the good stuff. For a young, healthy, pregnant woman or child, I would typically pick an antibiotic such as macrodantin that is not as strong, so that we do not develop too much resistance to ciprofloxacin, and it works when we need it to. So it sounds like your doctor is taking good care of you. Please rest assured that you did not have to do anything , so to speak, to get the urinary tract infection, and you can tell the others in your home that you are right. I hope that this has answered your question. Please feel free to check back if you have any further questions. Again - thank you for writing, and I hope you are feeling quite well.