Kidney Infection and Other UTIs

In healthy people, urine in the bladder is sterile—no bacteria or other infectious organisms are present. The tube that carries urine from the bladder out of the body (urethra) contains no bacteria or too few to cause an infection. However, any part of the urinary tract can become infected. An infection anywhere along the urinary tract is called a urinary tract infection (UTI).

UTIs are usually classified as upper or lower according to where they occur along the urinary tract, although it is sometimes difficult or impossible for doctors to make such a determination:

  • Lower UTIs: Infections of the bladder (cystitis)
  • Upper UTIs: Infections of the kidneys (pyelonephritis)

Some doctors also consider infections of the urethra (urethritis) and prostate (prostatitis) to be lower UTIs. In paired organs (such as the kidneys), infection can occur in one or both organs. UTIs can occur in children as well as in adults.

Causes

The organisms that cause infection usually enter the urinary tract by one of two routes. The most common route by far is through the lower end of the urinary tract—the opening of a man's urethra at the tip of the penis or the opening of a woman's urethra at the vulva. The infection ascends the urethra to the bladder, and sometimes to the kidneys, or both. The other possible route is through the bloodstream, usually to the kidneys.

UTIs are almost always caused by bacteria, although some viruses, fungi, and parasites can infect the urinary tract as well. More than 85% of UTIs are caused by bacteria from the intestine or vagina. Ordinarily, however, bacteria that enter the urinary tract are washed out by the flushing action of the bladder as it empties.

Bacteria

Bacterial infections of the lower urinary tract—usually the bladder—are very common, especially among young, sexually active women. Young women also often get bacterial kidney infections, but less commonly than bladder infections. Escherichia coli is the most common bacteria to cause a UTI. Among people between the ages of 20 and 50, bacterial UTIs are about 50 times more common among women than men. In men, the urethra is longer, so it is more difficult for bacteria to ascend far enough to cause an infection. In men between the ages of about 20 to 50, most UTIs are urethritis or prostatitis. In people older than 50, UTIs become more common among both men and women, with less difference between the sexes.

FACTORS CONTRIBUTING TO BACTERIAL URINARY TRACT INFECTIONS

Infections beginning in the urinary tract

  • Blockage (for example, by stones) anywhere in the urinary tract
  • Abnormal bladder function that prevents proper emptying, such as occurs in neurologic diseases
  • Leaking of the valve-like mechanism between the ureter and the bladder, allowing urine and bacteria to flow backward from the bladder up the ureters, possibly reaching the kidneys (more common among children who have a UTI)
  • Insertion of a urinary catheter or any instrument by a doctor
  • Sexual intercourse
  • Use of a diaphragm with spermicide
  • Presence of an abnormal connection (fistula) between the vagina and the bladder or the intestine and the bladder
  • Among men, prostate enlargement or infection

Infections spread to the urinary tract from the blood (uncommon)

  • Infection in the bloodstream (septicemia)
  • Infection of the heart valves (infective endocarditis, an uncommon cause)

Viruses

The herpes simplex virus type 2 (HSV-2) may infect the urethra, making urination painful and emptying of the bladder difficult. Other viral UTIs, such as bladder and kidney infections, do not usually develop unless a person's immune system is impaired (for example, by cancer, HIV/AIDS, or use of a drug that suppresses the immune system).

Fungi

Certain fungi, or yeasts, can infect the urinary tract. This type of infection is often called a yeast infection (yeasts can also cause inflammation of the vagina [vaginitis]). The fungus Candida is the organism most likely to cause urinary tract yeast infections. Candida frequently infects people who have an impaired immune system or a bladder catheter in place. Fungi and bacteria may infect the kidneys at the same time.

Parasites

A number of parasites, including certain types of worms, can infect the urinary tract.

Trichomoniasis, caused by a type of microscopic parasite, is a sexually transmitted disease that can cause a copious greenish yellow, frothy discharge from the vagina in women. Occasionally, the bladder or urethra becomes infected. Trichomoniasis can infect the urethra in men. It usually causes no symptoms.

Schistosomiasis, an infection caused by a type of worm called a fluke, can affect the kidneys, ureters, and bladder. This infection is a common cause of severe kidney failure among people who live in Africa, South America, and Asia. Persistent bladder schistosomiasis often causes blood in the urine or blockage of the ureters and may eventually result in bladder cancer.

Filariasis, a threadworm infection, obstructs lymphatic vessels, causing lymph fluid to enter the urine (chyluria). Filariasis can cause enormous swelling of tissues (elephantiasis), which, in men, may involve the scrotum.

 

Pyelonephritis is a bacterial infection of one or both kidneys.

  • Infection can spread up the urinary tract to the kidneys, or uncommonly the kidneys may become infected through bacteria in the bloodstream.
  • Chills, fever, back pain, nausea, and vomiting can occur.
  • Urine and sometimes blood and imaging tests are done if doctors suspect pyelonephritis.
  • Antibiotics are given to treat the infection.

Causes

Pyelonephritis is more common among women than men. Escherichia coli, a type of bacteria normally in the large intestine, causes about 90% of cases of pyelonephritis among people who are not hospitalized or living in a nursing home. Infections usually ascend from the genital area through the urethra to the bladder, up the ureters, into the kidneys. In a person with a healthy urinary tract, an infection is usually prevented from moving up the ureters into the kidneys by the flow of urine washing organisms out and by closure of the ureters at their entrance to the bladder. However, any physical blockage (obstruction) to the flow of urine, such as a structural abnormality, kidney stone, or an enlarged prostate gland, or the backflow (reflux) of urine from the bladder into the ureters increases the likelihood of pyelonephritis.

The risk of pyelonephritis is increased during pregnancy. During pregnancy, the enlarging uterus puts pressure on the ureters, which partially obstructs the normal downward flow of urine. Pregnancy also increases the risk of reflux of urine up the ureters by causing the ureters to dilate and reducing the muscle contractions that propel urine down the ureters into the bladder. Occasionally, a catheter that remains in the bladder can cause pyelonephritis by allowing bacteria to enter or remain in the bladder.

In about 5% of cases, infections are carried to the kidneys from another part of the body through the bloodstream. For instance, a staphylococcal skin infection can spread to the kidneys through the bloodstream.

The risk and severity of pyelonephritis are increased in people with diabetes or a weakened immune system (which reduces the body's ability to fight infection). Pyelonephritis is usually caused by bacteria, but rarely it is caused by tuberculosis (a rare bacterial cause of pyelonephritis), fungal infections, and viruses.

Some people develop long-standing infection (chronic pyelonephritis). Almost all of them have significant underlying abnormalities, such as a urinary tract obstruction, large kidney stones that persist, or, more commonly, reflux of urine from the bladder into the ureters (which occurs mostly in young children). Chronic pyelonephritis can cause bacteria to be released into the bloodstream, sometimes resulting in infections in the opposite kidney or elsewhere in the body. Rarely, chronic pyelonephritis can eventually severely damage the kidneys.

Symptoms

Symptoms of pyelonephritis often begin suddenly with chills, fever, pain in the lower part of the back on side, nausea, and vomiting.

About one third of people with pyelonephritis also have symptoms of cystitis, including frequent, painful urination. One or both kidneys may be enlarged and painful, and doctors may find tenderness in the small of the back on the affected side. Sometimes the muscles of the abdomen are tightly contracted. Irritation from the infection or the passing of a kidney stone (if one is present) can cause spasms of the ureters. If the ureters go into spasms, people may experience episodes of intense pain (renal colic). In children, symptoms of a kidney infection often are slight and more difficult to recognize (see Urinary Tract Infection in Children (UTI)). In older people, pyelonephritis may not cause any symptoms that seem to indicate a problem in the urinary tract. Instead, older people may have a decrease in mental function (delirium or confusion), fever, or an infection of the bloodstream (sepsis).

In chronic pyelonephritis, the pain may be vague, and fever may come and go or not occur at all.

Diagnosis

The typical symptoms of pyelonephritis lead doctors to do two common laboratory tests to determine whether the kidneys are infected: examining a urine specimen under a microscope to count the number of red and white blood cells and bacteria and a urine culture, in which bacteria from a urine sample are grown in a laboratory to identify the numbers and type of bacteria. Blood tests may be done to check for elevated white blood cell levels (suggesting infection), bacteria in the blood, or kidney damage.

Imaging tests are done in people who have intense back pain typical of renal colic, in those who do not respond to antibiotic treatment within 72 hours, in those whose symptoms return shortly after antibiotic treatment is finished, in those with long-standing or recurring pyelonephritis, in those whose blood test results indicate kidney damage, and in men (because they so rarely develop pyelonephritis). Ultrasonography or helical (spiral) computed tomography (CT) studies done in these situations may reveal kidney stones, structural abnormalities, or other causes of urinary obstruction.

Prognosis

Most people recover fully. Delayed recovery and the chance of complications are more likely if the person needs hospitalization, the infecting organism is resistant to commonly used antibiotics, or the person has a disorder that weakens the immune system (such as certain cancers, diabetes mellitus, or AIDS) or a kidney stone.

Prevention and Treatment

Antibiotics are started as soon as the doctor suspects pyelonephritis and samples have been taken for laboratory tests. The choice of drug or its dosage may be modified based on the laboratory test results (including culture results), how sick the person is, and whether the infection started in the hospital, where bacteria tend to be more resistant to antibiotics. Other factors that can alter the choice or dosage of drug include whether the person's immune system is impaired and whether the person has a urinary tract abnormality (such as an obstruction).

Outpatient treatment with antibiotics given by mouth is usually successful if the person has:

  • No nausea or vomiting
  • No signs of dehydration
  • No other disorders that weaken the immune system, such as certain cancers, diabetes mellitus, or AIDS
  • No signs of very severe infection, such as low blood pressure or confusion
  • Pain that is controlled with drugs taken by mouth

Otherwise, the person is usually treated initially in the hospital. If hospitalization is needed and the person needs antibiotics, the antibiotics are given intravenously for 1 or 2 days, then they can usually be given by mouth.

Antibiotic treatment of pyelonephritis is given for 5 to14 days so that infection will not recur. However, antibiotic therapy may continue for up to 6 weeks for men in whom the infection is due to prostatitis, which is more difficult to eradicate. A final urine sample is usually taken shortly after the antibiotic treatment is finished to make sure the infection has been eradicated.

Surgery is necessary only occasionally if tests show that something is chronically blocking the urinary tract, such as a structural abnormality or a particularly large stone. Removal of the infected kidney may be necessary for people with chronic pyelonephritis who are about to undergo kidney transplantation. Spread of infection to the transplanted kidney is particularly risky because the person takes immunosuppressant drugs, which prevent rejection of the transplanted kidney but also weaken the body's ability to fight infection.

People who have frequent episodes of pyelonephritis or whose infection returns after antibiotic treatment is finished may be advised to take a small dose of antibiotic on a long-term basis. The ideal duration of such therapy is unknown. If the infection returns, preventive therapy may be continued indefinitely. If a woman of child-bearing age is taking an antibiotic, she should avoid pregnancy or talk to her doctor about whether to use an antibiotic that is safe during pregnancy in case she becomes pregnant.

 

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