urinary tract infections are the most frequent bacterial infection in women. they occur most frequently between the ages of 16 and 35 years. ten percent of women get an infection yearly; 60% have an infection at some point in their lives. nearly half of people get a second infection within a year. urinary tract infections occur four times more frequently in females than males. pyelonephritis (a kidney infection) occurs between 20–30 times less frequently than bladder infections. pyelonephritis is the most common cause of hospital acquired infections, accounting for approximately 40% of hospital-acquired infections. rates of asymptomatic bacteria in the urine increase with age from 2% to 7% in women of childbearing age to as high as 50% in elderly women in care homes. rates of aysmtomatic bacteria in the urine among men over 75 are 7-10%.