I. What is a urinary tract infection? Urinary tract infections (UTIs) are common diseases of the urinary tract that occur in about half of women at some point in their lives and are caused by the invasion of pathogenic microorganisms into the urinary tract system, such as the kidneys, bladder and various tubes that connect them. If treated promptly, the most common bladder infections are usually not serious. However, if the infection spreads to the kidneys, the situation is often very serious. Symptoms of UTI: Bladder infection is the most common type of UTI. Symptoms include painful urination, burning urination, urgency, pain in the small abdomen, cloudy or smelly urine, and very few patients have no symptoms. Kidney infection, untreated or poorly controlled bladder infection can spread upstream to the kidneys, manifested by affected back pain, fever and chills, nausea and vomiting.