Blockage (for example, by stones) anywhere in the urinary tract

Abnormal bladder function that prevents proper emptying, such as occurs in neurologic diseases

Leaking of the valve-like mechanism between the ureter and the bladder, allowing urine and bacteria to flow backward from the bladder up the ureters, possibly reaching the kidneys (more common among children who have a UTI)

Insertion of a urinary catheter or any instrument by a doctor

Sexual intercourse

Use of a diaphragm with spermicide

Presence of an abnormal connection (fistula) between the vagina and the bladder or the intestine and the bladder

Among men, prostate enlargement or infection of the prostate

Infection in the bloodstream (septicemia)

Infection of the heart valves (infective endocarditis, an uncommon cause)