Urinary tract infection (UTI) is a bacterial infection that affects any part of the urinary tract. Symptoms include frequent feeling and/or need to urinate, pain during urination, and cloudy urine. The main causal agent is Escherichia coli. Although urine contains a variety of fluids, salts, and waste products, it does not usually have bacteria in it. When bacteria get into the bladder or kidney and multiply in the urine, they may cause a UTI.The most common type of UTI is acute cystitis often referred to as a bladder infection. An infection of the upper urinary tract or kidney is known as pyelonephritis, and is potentially more serious. Although they cause discomfort, urinary tract infections can usually be easily treated with a short course of antibiotics with all no significant difference between the classes of antibiotics commonly used.Signs and symptomsThe most common symptoms of a bladder infection are burning with urination (dysuria), frequency of urination, an urge to urinate, no vaginal discharge, and no significant pain. An upper urinary tract infection or pyelonephritis may also present with flank pain and a fever. Healthy women have an average of 5 days of symptoms.The symptoms of urinary tract infections may vary with age and the part of the urinary system that was affected. In young children, urinary tract infection symptoms may include diarrhea, loss of appetite, nausea and vomiting, fever, and excessive crying that cannot be resolved by typical measures. Older children on the other hand may experience abdominal pain, or incontinence. Lower urinary tract infections in adults may manifest with symptoms including hematuria (blood in the urine), inability to urinate despite the urge, and malaise.Other signs of urinary tract infections include foul-smelling urine and urine that appears cloudy.Depending on the site of infection, urinary tract infections may cause different symptoms. Urethritis, meaning only the urethra has been affected, does not usually cause any other symptoms besides dysuria. However, if the bladder is affected (cystitis), the patient is likely to experience more symptoms, including lower abdomen discomfort, low-grade fever, pelvic pressure, and frequent urination, all together with dysuria.Whereas in newborns the condition may cause jaundice and hypothermia, in the elderly, symptoms of urinary tract infections may include lethargy and a change in mental status, signs that are otherwise nonspecific.