Category A - full version without watermark 720x576 (check terms and conditions at The version with watermark is for free to embed . Cystitis is inflammation of the urinary bladder. The condition more often affects women, but can affect either sex and all age groups.More than 85% of cases of cystitis are caused by Escherichia coli, a bacterium found in the lower gastrointestinal tract. Sexual intercourse may increase the risk of cystitis because bacteria can be introduced into the bladder through the urethra during sexual activity. Once bacteria enter the bladder, they are normally removed through urination. When bacteria multiply faster than they are removed by urination, infection results.