Urinary tract infections usually develop first in the lower urinary tract (urethra, bladder) and, if not treated, progress to the upper urinary tract (ureters, kidneys).
- Bladder infection (cystitis) is by far the most common UTI.
- Infection of the urethra is called urethritis.
- Kidney infection (pyelonephritis) requires urgent treatment and can lead to reduced kidney function and possibly even death in untreated, severe cases.
Most urinary tract infections are caused by bacteria. Any part of your urinary tract can become infected. The urinary tract includes the kidneys, ureters, bladder and urethra. Bladder infections are the most common.
Normally, urine is sterile. It is usually free of bacteria, viruses, and fungi but does contain fluids, salts, and waste products. An infection occurs when tiny organisms, usually bacteria from the digestive tract, cling to the opening of the urethra and begin to multiply. The urethra is the tube that carries urine from the bladder to outside the body. Most infections arise from one type of bacteria, Escherichia coli (E. coli), which normally lives in the colon.
In many cases, bacteria first travel to the urethra. When bacteria multiply, an infection can occur. An infection limited to the urethra is called urethritis. If bacteria move to the bladder and multiply, a bladder infection, called cystitis, results. If the infection is not treated promptly, bacteria may then travel further up the ureters to multiply and infect the kidneys. A kidney infection is called pyelonephritis.
Microorganisms called Chlamydia and Mycoplasma may also cause UTIs in both men and women, but these infections tend to remain limited to the urethra and reproductive system. Unlike E. coli, Chlamydia and Mycoplasma may be sexually transmitted, and infections require treatment of both partners.
The urinary system is structured in a way that helps ward off infection. The ureters and bladder normally prevent urine from backing up toward the kidneys, and the flow of urine from the bladder helps wash bacteria out of the body. In men, the prostate gland produces secretions that slow bacterial growth. In both sexes, immune defenses also prevent infection. But despite these safeguards, infections still occur.
To find out whether you have a UTI, your doctor will test a sample of urine for pus and bacteria. You will be asked to give a "clean catch" urine sample by washing the genital area and collecting a "midstream" sample of urine in a sterile container. This method of collecting urine helps prevent bacteria around the genital area from getting into the sample and confusing the test results. Usually, the sample is sent to a laboratory, although some doctors' offices are equipped to do the testing.
In the urinalysis test, the urine is examined for white and red blood cells and bacteria. Then the bacteria are grown in a culture and tested against different antibiotics to see which drug best destroys the bacteria. This last step is called a sensitivity test.
Some microbes, like Chlamydia and Mycoplasma, can be detected only with special bacterial cultures. A doctor suspects one of these infections when a person has symptoms of a UTI and pus in the urine, but a standard culture fails to grow any bacteria.
When an infection does not clear up with treatment and is traced to the same strain of bacteria, the doctor may order some tests to determine if your system is normal. One of these tests is an intravenous pyelogram, which gives x-ray images of the bladder, kidneys, and ureters. An opaque dye visible on x-ray film is injected into a vein, and a series of x rays is taken. The film shows an outline of the urinary tract, revealing even small changes in the structure of the tract.
If you have recurrent infections, your doctor also may recommend an ultrasound exam, which gives pictures from the echo patterns of soundwaves bounced back from internal organs. Another useful test is cystoscopy. A cystoscope is an instrument made of a hollow tube with several lenses and a light source, which allows the doctor to see inside the bladder from the urethra.Possible Signs of a Bladder Infection
Symptoms of UTI in young children include the following:
- Excessive crying that cannot be resolved by typical measures (e.g., feeding, holding)
- Loss of appetite
- Nausea and vomiting
Older children may experience the following symptoms with UTI:
- Flank or lower back pain (with a kidney infection)
- Frequent urination
- Inability to produce more than a small amount of urine at a time
- Pain in the abdomen or pelvic area
- Painful urination (dysuria)
- Urine that is cloudy or has an unusual smell
Symptoms of lower UTI (e.g., cystitis, urethritis) in adults include the following:
- Back pain
- Blood in the urine (hematuria)
- Cloudy dark or bloody urine
- Inability to urinate despite the urge
- Feeling like you need to urinate more often than usual
- Feeling the urge to urinate but not being able to
- Urine that smells bad
- General discomfort (malaise)
- Painful urination, burning sensation when you urinate (dysuria)
Symptoms that indicate upper UTI (e.g., pyelonephritis) in adults include the following:
- High fever
- Pain below the ribs
Hormonal changes and shifts in the urinary tract during pregnancy increase the risk for kidney infection. Prenatal care includes regular urine testing because bacteria are often present without causing symptoms and UTI during pregnancy may result in complications (e.g., premature birth, high blood pressure) for the mother and fetus. Diseases that suppress the immune system (e.g., HIV) and debilitating diseases (e.g., cancer, sickle cell anemia) increase the risk for UTIs and complications.