The treatment of UTI is best guided by the results of cultures and antimicrobial suscepti-bility tests. In simple isolated instances of cystitis in a young woman, the etiology is of-ten assumed to be E. coli and the antimicrobic selected empirically based on knowledge of the susceptibility of local strains. Sulfonamides and trimethoprim alone or in combination with sulfamethoxazole, a fluoroquinolone, and nitrofurantoin are the agents most commonly used. In most areas, the use of ampicillin is precluded by resistance rates ex-ceeding 25%. For children and patients with risk factors or recurrent infections, empiric therapy should always be confirmed by culture and susceptibility testing. Likewise, the duration of therapy depends on the severity of the infection and the risk status of the pa-tient. Success of treatment may be tested by a follow-up urine culture 1 to 2 weeks after therapy is completed.
Those with several symptomatic episodes annually may be helped with long-term, low-dose chemoprophylaxis. In women whose recurrences are related to sexual activity, admin-istration of the chemoprophylactic agent may be limited to immediately after intercourse. Infected children, men, and those who experience UTI relapse should be investigated with intravenous pyelography to allow detection and correction of any factor causing predisposition to infection.