Urinary tract infection (UTI) is an infection caused by the introduction of bacteria into the urinary tract.

The urinary tract includes the following organs:

• Kidneys (which create urine by removing extra water and waste from the blood)
  
  
• Ureters (tubes that transfer urine from the kidneys to the bladder)
  
  
• Bladder (where urine is stored)
  
  
• Urethra (tube that empties the bladder during urination)

Urine that travels through the urinary tract is normally sterile, containing only salts, fluids and waste products. Both the lining of the bladder and urine have antibacterial properties as well, which makes it difficult for bacteria to grow. However, if too much bacteria is introduced into the urinary tract, it can overwhelm the body’s natural germ-fighting capabilities, allowing infection to set in. Certain people with weakened immune systems (e.g., patients with diabetes, elderly people) have a decreased ability to clear bacteria from their urinary tract.

UTIs occur when microorganisms – usually a type of bacteria called Escherichia coli (E. coli) or staphylococcus saprophyticus – adhere to the opening of the urethra and start to multiply. Bacteria gain access to the urinary tract through the urethra.

Infection may occur anywhere within the urinary tract. A UTI that affects the urethra is called urethritis. If this condition is not treated immediately, bacteria can travel through the urethra to the bladder, causing a bladder infection or cystitis. If cystitis is not treated promptly, the bacteria can spread to the kidneys, resulting in pyelonephritis (kidney infection), the most serious type of UTI. The majority of UTIs affect the bladder.

Infection does not always occur when bacteria enter the bladder. Normally, the body removes bacteria through urination, without producing any symptoms of infection. It is important to note that the presence of bacteria in the urine does not always indicate an infection. Some individuals, especially older adults, have bacteria in the bladder that does not cause any signs or symptoms. This condition, known as asymptomatic bacteriuria, does not typically pose any health risks. However, certain groups (e.g., pregnant women) are at a greater risk for kidney infection if they develop this condition and may need to be treated with antibiotics.

UTIs account for almost 10 million doctor visits every year, according to the National Kidney Foundation. UTIs may occur in both genders and all age groups, although they are more common in women and older adults.

UTIs can be painful and irritating. Left untreated, these infections can spread to the kidneys and bloodstream, causing serious health problems, such as acute or chronic kidney infection or sepsis, a life-threatening blood infection. Additional complications of UTIs include abscesses (collections of pus) and inflammation of the bladder wall. These most often occur in patients with diabetes.

Although symptoms such as burning, frequent urination and urinary urgency are common symptoms of UTIs, they may also indicate the presence of another condition called urethral syndrome. Urethral syndrome is the name given to a group of symptoms that affect the bladder, but cannot be attributed to a specific cause (e.g., bacterial infection). Only a physician can determine whether UTI or urethral syndrome is present.

Additionally, a condition known as interstitial cystitis is an inflammation of the bladder wall that can cause symptoms that mimic UTI, but is not related to an infection. People who continue to experience symptoms of an infection, despite cultures indicating no infection, should be evaluated by a urologist to determine if they have this condition.