The upper urinary tract is composed of the kidneys and ureters. An upper urinary tract infection is generally pyelonephritis or a kidney infection, which is a more serious condition that requires intensive treatment. The lower urinary tract consists of the bladder and the urethra. These infections are caused by different organisms. Children and adults alike can get UTIs.
Older men develop UTIs when an enlarged prostate blocks the flow of urine.
These bacteria gain access to the bladder via the urethra. The infection can spread further as the bacteria move from the bladder via the ureters, leading to a kidney infection. In normal healthy people, the skin surrounding the opening of the urethra is inhabited by bacteria that do not infect the urinary tract. Occasionally, infection still occurs. In women, sexual intercourse can introduce larger numbers of bacteria into the bladder, giving us the term honeymoon cystitis .