What causes UTIs?
The vast majority of UTIs are caused by Escherichia coli (E. coli), a bacteria usually found in the digestive system. Chlamydia and mycoplasma bacteria can infect the urethra but not the bladder. UTIs occur when these microbes enter your kidneys, ureters, urinary bladder and urethra.
People of any age and sex can develop UTIs. However, UTI is very common in teens and young women because the female urethra is shorter and closer to the anus.
Types of UTIs include:
- Lower tract infections: These involve the urethra and urinary bladder (cystitis). Bacteria in the intestine is the main cause of lower UTIs. The bacteria spread from the anus to the urethra and bladder, where they grow, invade the tissue and cause infection.
- Upper tract infections: These involve the ureters and kidneys (pyelonephritis) and require hospitalization. Upper UTIs usually occur when bacteria travel up from the bladder into the kidneys. Sometimes, they occur when bacteria travel from other areas of the body through the bloodstream and settle in the kidneys. This is common in the elderly, people with diabetes and those with poor immunity.