Kidney Infections Health Article

Definition

Kidney infection is a general term used to describe infection of the kidney by bacteria, fungi, or viruses. The infecting microbe may have invaded the kidney from the urinary bladder or from the bloodstream. The disease is characterized by fever, chills, back pain, and, often, the symptoms associated with bladder infection.

Description

As the principle part of the urinary system, the kidneys process the fluid component of blood (called plasma) to maintain appropriate water volume and concentrations of chemicals. The waste product formed from this process is called urine. Urine travels from the kidney, through tubes called ureters, to the urinary bladder, and is eliminated from the body through a tube called the urethra. The kidneys and ureters comprise the upper urinary tract, and the bladder and urethra comprise the lower urinary tract.

Kidney infection, also called pyelonephritis and upper urinary tract infection, occurs when microbes, usually bacteria, invade the tissues of the kidney and multiply. One or both kidneys may be infected. Infection originating directly from the bladder is called an ascending infection.

Inflammation occurs in response to the infection. As a result of the infection and inflammation, scarring and other tissue damage may occur. Most cases of acute kidney infection resolve without any permanent kidney damage. In severe cases, kidney damage is so extensive that the kidneys can no longer function, a state called renal failure.

Types of kidney infections:

• Acute pyelonephritis: uncomplicated kidney infection that has a short and relatively severe course.
• Chronic pyelonephritis: long-standing disease associated with either active or inactive (healed) kidney infection.
• Emphysematous pyelonephritis: acute infection associated with gas in and around the kidney. This type almost always occurs in persons with diabetes.
• Pyonephrosis: acute or chronic pyelonephritis associated with blockage of the ureter.
• Renal and perinephric abscesses: abscesses (pockets of pus) in and around the kidney.

Kidney infections occur most often in adult females who are otherwise healthy. Urinary tract infections are uncommon in males until old age, when bladder catheterization and other urinary procedures are more commonly performed.

Causes & symptoms

Kidney infection is usually caused by bacteria, although infection by fungi (yeasts and molds) or viruses does occur. The bacteria Escherichia coli (E. coli) is responsible for about 85% of the cases of acute pyelonephritis. Other common causes include Klebsiella, Enterobacter, Proteus, Enterococcus, and Pseudomonas species. Infection by Proteus species can lead to the formation of stones. E. coli causes only 60% of the acute pyelonephritis cases in the elderly. Kidney infection may also be caused by Mycobacterium tuberculosis or other Mycobacterium species or by the yeast Candida. Kidney infection can be caused by Group B streptococci in newborns.

Certain women are inherently more susceptible to urinary tract infections. Researchers have found that women who have recurrent infections possess certain markers on their blood cells. Also, the bacteria which commonly cause urinary tract infections stick more readily to the vaginal cells of women who have recurrent infections. Other risk factors for kidney disease include:

• bladder catheterization or instrumentation
• diabetes
• pregnancy
• urinary calculi (stones)
• urinary tract abnormalities
• urinary tract obstruction

The symptoms of kidney infection include fever, shaking chills, nausea, vomiting, and middle to lower back pain which may travel to the abdomen and groin. This pain may be severe. These symptoms may be preceded or accompanied by those associated with bladder infection—frequent, painful urination.

Infants and young children may show fever, irritability, straining on urination, and urine odor. Fewer than half of newborns have fever associated with kidney infection, which makes diagnosis difficult.

In more than 20% of elderly patients with kidney infection, the presenting symptoms are gastrointestinal or pulmonary (lung). Also, one-third of elderly patients do not develop fever.

Diagnosis

Kidney infections can be diagnosed by family doctors, OB/GYN doctors, and urologists (doctors who specialize in the urinary system). The diagnosis of kidney infection is based primarily on symptoms, urinalysis, and urine cultures. Blood tests may also be performed. Approximately 20% of patients have bacteria in the bloodstream, a condition called bacteremia. Urine dipsticks that detect signs of infection are often used right in the doctor's office. Urine would be examined with a microscope for the presence of bacteria and leukocytes (white blood cells). Urine culture would identify which microbe is causing the infection and may also be used to determine which antibiotic would be effective.

Other routine diagnostic procedures to look for signs of infection in the kidney may be used. An x ray of the abdomen may be taken. Ultrasound, which uses sound waves to visualize internal organs, may be used to examine the bladder and kidney. Less routinely performed are intravenous urograms, computerized tomography (CT scan), and scintillation scans.