A urinary tract infection (UTI) is an infection involving the kidneys, ureters, bladder, or urethra. These are the structures that urine passes through before being eliminated from the body.
The kidneys are a pair of small organs that lie on either side of the spine at about waist level. They have several important functions in the body, including removing waste and excess water from the blood and eliminating them as urine. These functions make them important in the regulation of blood pressure. Kidneys are also very sensitive to changes in blood sugar levels and blood pressure and electrolyte balance. Both diabetes and hypertension can cause damage to these organs.
Two ureters, narrow tubes about 10 inches long, drain urine from each kidney into the bladder.
The bladder is a small saclike organ that collects and stores urine. When the urine reaches a certain level in the bladder, we experience the sensation that we have to void, then the muscle lining the bladder can be voluntarily contracted to expel the urine.
The urethra is a small tube connecting the bladder with the outside of the body. A muscle called the urinary sphincter, located at the junction of the bladder and the urethra, must relax at the same time the bladder contracts to expel urine.
Any part of this system can become infected. As a rule, the farther up in the urinary tract the infection is located, the more serious it is.
The upper urinary tract is composed of the kidneys and ureters. Infection in the upper urinary tract generally affects the kidneys (pyelonephritis), which can cause fever, chills, nausea, vomiting, and other severe symptoms.
The lower urinary tract consists of the bladder and the urethra. Infection in the lower urinary tract can affect the urethra (urethritis) or the bladder (cystitis).
In the United States, urinary tract infections account for more than 10 million visits to medical offices and hospitals each year.
Urinary tract infections are much more common in adults than in children, but about 1%-2% of children do get urinary tract infections. Urinary tract infections in children are more likely to be serious than those in adults (especially in younger children).
Urinary tract infection is the most common urinary tract problem in children besides bedwetting.
Urinary tract infection is second only to respiratory infection as the most common type of infection.
These infections are much more common in girls and women than in boys and men younger than 50 years of age. The reason for this is not well understood, but anatomic differences between the genders (a shorter urethra in women) might be partially responsible.
About 40% of women and 12% of men have a urinary tract infection at some time in their life.
Causes and Risk Factors
The urine is normally sterile. An infection occurs when bacteria get into the urine and begin to grow. The bacterial infection usually starts at the opening of the urethra where the urine leaves the body and moves upward into the urinary tract.
The culprit in at least 90% of uncomplicated infections is a type of bacteria called Escherichia coli, better known as E. coli. These bacteria normally live in the bowel (colon) and around the anus.
These bacteria can move from the area around the anus to the opening of the urethra. The two most common causes of this are improper wiping and sexual intercourse.
Usually, the act of emptying the bladder (urinating) flushes the bacteria out of the urethra. If there are too many bacteria, urinating may not stop their spread.
The bacteria can travel up the urethra to the bladder, where they can grow and cause an infection.
The infection can spread further as the bacteria move up from the bladder via the ureters.
If they reach the kidney, they can cause a kidney infection (pyelonephritis), which can become a very serious condition if not treated promptly.
The following people are at increased risk of urinary tract infection:
People with conditions that block (obstruct) the urinary tract, such as kidney stones
People with medical conditions that cause incomplete bladder emptying (for example, spinal cord injury)
Postmenopausal women: Decreased circulating estrogen makes the urinary tract more vulnerable to a UTI.
People with suppressed immune systems: Examples of situations in which the immune system is suppressed are HIV/AIDS and diabetes. People who take immunosuppressant medications such as chemotherapy for cancer also are at increased risk.
Women who are sexually active: Sexual intercourse can introduce larger numbers of bacteria into the bladder. Urinating after intercourse seems to decrease the likelihood of developing a urinary tract infection.
Women who use a diaphragm for birth control
Men with an enlarged prostate: Prostatitis or obstruction of the urethra by an enlarged prostate can lead to incomplete bladder emptying, thus increasing the risk of infection. This is most common in older men.
Breastfeeding has been found to decrease the risk for urinary tract infections in children.
The following special groups may be at increased risk of urinary tract infection:
Very young infants: Bacteria gain entry to the urinary tract via the bloodstream from other sites in the body.
Young children: Young children have trouble wiping themselves and washing their hands well after a bowel movement. Poor hygiene has been linked to an increased frequency of urinary tract infections.
Children of all ages: Urinary tract infection in children can be (but is not always) a sign of an abnormality in the urinary tract, usually a partial blockage. An example is a condition in which urine moves backward from the bladder up the ureters (vesicoureteral reflux).
Hospitalized patients or nursing-home residents: Many of these individuals are catheterized for long periods and are thus vulnerable to infection of the urinary tract. Catheterization means that a thin tube (catheter) is placed in the urethra to drain urine from the bladder. This is done for people who have problems urinating or cannot reach a toilet to urinate on their own.
Patients using catheters: If a patient is required to empty their bladder using a catheter, they are at increased risk for infection.
Symptoms of UTIs
Lower urinary tract infection (infections of the bladder or urethra)
Bladder (cystitis, or bladder infection): The lining of the urethra and bladder becomes inflamed and irritated.
Dysuria: pain or burning during urination
Frequency: more frequent urination (or waking up at night to urinate, sometimes referred to as nocturia); often with only a small amount of urine
Urinary urgency: the sensation of having to urinate urgently
Cloudy, bad-smelling, or bloody urine
Lower abdominal pain or pelvic pressure or pain
Mild fever (less than 101 F), chills, and “just not feeling well” (malaise)
Urethra (urethritis): Burning with urination
Upper urinary tract infection (pyelonephritis, or kidney infection)
Symptoms develop rapidly and may or may not include the symptoms for a lower urinary tract infection.
Fairly high fever (higher than 101 F)
Flank pain: pain in the back or side, usually on only one side at about waist level
In newborns, infants, children, and elderly people, the classic symptoms of a urinary tract infection may not be present. Other symptoms may indicate a urinary tract infection.
Newborns: fever or hypothermia (low temperature), poor feeding, jaundice
Infants: vomiting, diarrhea, fever, poor feeding, not thriving
Children: irritability, eating poorly, unexplained fever that doesn’t go away, loss of bowel control, loose bowels, change in urination pattern
Elderly people: fever or hypothermia, poor appetite, lethargy, change in mental status
Pregnant women are at increased risk for an UTI. Typically, pregnant women do not have unusual or unique symptoms. If a woman is pregnant, her urine should be checked during prenatal visits because an unrecognized infection can cause pregnancy health complications.
Although most people have symptoms with a urinary tract infection, some do not.
The symptoms of urinary tract infection can resemble those of sexually transmitted diseases.
Diagnosis of a urinary tract infection is based on information someone gives about his or her symptoms, medical and surgical history, medications, habits, and lifestyle. A physical examination and lab tests complete the evaluation.
A health care professional may simply perform a urine dipstick test in the office. Only a few minutes are needed to obtain results. Your health-care provider may also send a urine sample to the lab for culture testing (see below). These results take a few days to come back. This tells the doctor the exact bacteria causing the infection and to which antibiotics these bacteria have resistance or sensitivity. The culture is usually sent for special populations, including men, because they are less likely to get UTIs. It is not necessary to send a culture for everyone because the majority of UTIs are caused by the same bacteria.
The single most important lab test is urinalysis. A urine culture will be tested for signs of infection, such as the presence of white blood cells and bacteria.
In certain circumstances, urine also may be “cultured.” This means that a small amount of the urine is brushed on a sterile nutrient substance in a plastic plate. The plate is allowed to sit for a few days and then examined to see what kind of bacteria are growing on it. These bacteria are treated with different antibiotics to see which works best against them. This helps determine the best treatment for the specific infection.
Blood tests usually are not required unless a complicated condition, such as pyelonephritis or kidney failure, is suspected.
For a culture specimen, the patient will be asked to give a clean-catch, midstream urine specimen. This avoids contamination of the urine with bacteria from the skin. Patients will be instructed in how to do this.
Midstream means urinating a little into the toilet before collecting a specimen. The idea is to avoid collecting the urine that comes out first, as this urine is often contaminated.
Clean-catch refers to a midstream sample that was collected after cleaning the area of the urethral opening.
Adult women and older girls: Cleanse the area around the urethral opening gently (but completely) using a sterile wipe or soap and water. Catch the urine midstream. For some women, catheterization (inserting a tube into the bladder) may be the only way to obtain a sterile, uncontaminated specimen.
Men and boys: A sterile specimen can usually be obtained with a midstream catch. Uncircumcised males should retract the foreskin and cleanse the area before urinating.
Newborns: Urine may be obtained with a catheter or a procedure in which a needle is introduced through the lower abdominal wall to draw (aspirate) urine from the bladder.
Infants and children: Either catheterization or the needle aspiration method is used.
If someone cannot produce a urine specimen or is unable to follow instructions for a clean-catch specimen, a health-care professional may obtain a urine specimen by catheterization.
This means placing a thin tube (catheter) in the urethra to drain urine from the bladder.
The catheter usually is removed after the bladder is emptied.
The catheter may remain in place if someone is very ill or if it is necessary to collect all urine or measure urine output.
Depending on their symptoms, sexually active women could require a pelvic examination because pelvic infections can have similar symptoms as a urinary tract infection. Males will require a genital examination, and depending on the symptoms, most likely a prostate examination. A prostate infection (prostatitis) requires a longer course of antibiotics than a urinary tract infection.
Men will most likely require a rectal examination so that the prostate can be checked. A prostate infection (prostatitis) requires a longer course of antibiotics than a urinary tract infection.
Rarely, an imaging test may be indicated to detect any underlying problem in the urinary tract that could cause an infection. This is usually only necessary in repeat infections or special circumstances (unusual bacteria, suspected anatomic abnormalities).
An ultrasound examination can evaluate kidney and bladder problems.
A fluoroscopic study can show any physical problems that predispose children to urinary tract infections.
Intravenous pyelogram (IVP) is a special series of X-rays that uses a contrast dye to highlight abnormalities in the urinary tract.
Cystoscopy involves insertion of a thin, flexible tube with a tiny camera on the end through the urethra into the bladder. This allows detection of abnormalities inside the bladder that might contribute to infections.
A CT scan gives a very detailed three-dimensional picture of the urinary tract.
Imaging tests are most often needed for the following groups:
Children with repeat urinary tract infections, especially boys
Up to 50% of infants and 30% of older children with a urinary tract infection have an anatomic abnormality. The child’s pediatrician should investigate this possibility.
Adults with frequent or recurrent urinary tract infections
People who have blood in the urine
You can prevent getting another UTI with the following tips:
Empty your bladder frequently as soon as you feel the need to go; don’t rush, and be sure you’ve emptied your bladder completely.
Wipe from front to back.
Drink lots of water.
Choose showers over baths.
Stay away from feminine hygiene sprays, scented douches, and scented bath products — they’ll only increase irritation.
Cleanse your genital area before sex.
Urinate after sex to flush away any bacteria that may have entered your urethra.
If you use a diaphragm, unlubricated condoms, or spermicidal jelly for birth control, consider switching to another method. Diaphragms can increase bacteria growth, while unlubricated condoms and spermicides can cause irritation. All can make UTI symptoms more likely.
Keep your genital area dry by wearing cotton underwear and loose-fitting clothes. Avoid tight jeans and nylon underwear — they can trap moisture, creating the perfect environment for bacteria growth.
The usual treatment for both simple and complicated urinary tract infections is antibiotics. The type of antibiotic and duration of treatment depend on the circumstances. Examples of common antibiotics used in treatment include, but are not limited to, amoxicillin, sulfamethoxazole/trimethoprim (Bactrim), ciprofloxacin, nitrofurantoin (Macrobid), and many others. Your health-care provider will chose the appropriate medication for your condition and the specific causative organisms.
Lower urinary tract infection (cystitis, or bladder infection)
In an otherwise healthy person, a three-day course of antibiotics is usually enough. Some providers prefer a seven-day course of antibiotics. Occasionally, a single dose of an antibiotic is used. A health-care professional will determine which of these options is best.
In adult males, if the prostate is also infected (prostatitis), four weeks or more of antibiotic treatment may be required.
Adult females with potential for or early involvement of the kidneys, urinary tract abnormalities, or diabetes are usually given a five- to seven-day course of antibiotics.
Children with uncomplicated cystitis are usually given a 10-day course of antibiotics.
To alleviate burning pain during urination, phenazopyridine (Pyridium) or a similar drug, can be used in addition to antibiotics for one to two days.
Upper urinary tract infection (pyelonephritis)
Young, otherwise healthy patients with symptoms of pyelonephritis can be treated as outpatients. They may receive IV fluids and antibiotics or an injection of antibiotics in the emergency department, followed by 10-14 days of oral antibiotics. They should follow up with their health-care professional in one to two days to monitor improvement.
If someone is very ill, dehydrated, or unable to keep anything in his or her stomach because of vomiting, an IV will be inserted into the arm. He or she will be admitted to the hospital and given fluids and antibiotics through the IV until he/she is well enough to switch to an oral antibiotic.
A complicated, acute infection may require treatment for several weeks.
A person may be hospitalized if he or she has symptoms of pyelonephritis and any of the following:
Appear very ill
Have not gotten better with outpatient antibiotic treatment
Have underlying diseases that compromise the immune system (diabetes is one example) or are taking immunosuppressive medication
Are unable to keep anything in the stomach because of nausea or vomiting
Had previous kidney disease, especially pyelonephritis, within the last 30 days
Have a device such as a urinary catheter in place
Have kidney stones
Urethritis in men and women can be caused by the same bacteria as sexually transmitted diseases (STDs). Therefore, people with symptoms of STDs (vaginal or penile discharge, for example) should be treated with appropriate antibiotics. Your doctor will have to evaluate you for STDs as well as UTIs if you experience any pain in the genital area.
Prognosis of UTIs
For people with uncomplicated cystitis or pyelonephritis, antibiotic treatment usually brings complete resolution of the infection.
If not treated promptly, urinary tract infections can cause permanent scarring of the urinary tract.
Recurrent urinary tract infections can become a problem and will require close monitoring by your health care provider.
Pyelonephritis, if not treated promptly, can spread to the bloodstream and cause a very severe infection.
Short-term and long-term kidney damage can be a result of pyelonephritis.
Death from pyelonephritis is rare in otherwise healthy people.
Factors associated with poor outcome are old age or general debility, kidney stones, recent hospitalization, diabetes, sickle cell disease, cancer, or chronic kidney disease.