UTIs can affect any person at any age but certain groups are at greater risk.
The main reason women are more susceptible to UTI's is due to their anatomy. The female urethra, is shorter than in a man, and it is also close to the anus from where bacteria can invade the urinary tract. In women, estrogen hormone levels also decline with age. This can cause the walls of the urinary tract to become thinner and dryer. The protective mucous membrane, or mucosa, also becomes less acidic which reduces its ability to fight infection. This is why estrogen hormone treatment may be recommended to prevent UTIs.
Other example of people at risk are the elderly, people with diabetes mellitus, a person with an indwelling catheter, and residents and patients.
Not being able to empty the bladder properly can increase the risk of a UTI since bacteria can grow in the remaining urine. Some causes for residual urine are constipation, outflow obstruction caused by an enlarged prostate or a prolapse, spinal cord injury and nerve damage which interferes with the normal function of the urinary tract.