The main symptom of cystitis (inflammation of the bladder) and urethritis (inflammation of the urethra) is the frequent and desperate need to urinate, accompanied by an agonizing burning sensation, a feeling of incomplete emptying of the bladder and occasional blood in the urine. The most frequent cause is infection by transfer the common colon bacillus E. coli from the large intestine to the bladder. Bruising and the presence of irritants may also trigger the disease. Cystitis in women often begins during a period of intense sexual activity, and may then develop following any sexual intercourse. There are also forms of sterile (non-infective) cystitis, the most common of which is interstitial cystitis or painful bladder disease.