Kidney infection (pyelonephritis) is a specific type of urinary tract infection (UTI) that generally begins in your urethra or bladder and travels up into your kidneys. If not treated properly, kidney infection can permanently damage your kidneys or spread to your bloodstream and cause a life-threatening infection. Prompt medical attention is required.

Kidney infection typically occurs when bacteria enter your urinary tract through the urethra and begin to multiply. Bacteria from an infection elsewhere in your body also can spread through your bloodstream to your kidneys.
However, bacteria in the urine don't always signify an infection. Some people, especially older adults, may have bacteria in the bladder that don't cause any signs or symptoms or harm, and therefore doesn't require treatment. Your kidneys have anti-biotic properties that ordinarily inhibit the growth of bacteria, however certain factors increase the chances that bacteria will enter your urinary tract:

• Women have a greater risk of kidney infection than do men. A woman's urethra is much shorter than a man's, so bacteria have less distance to travel from outside the body to the bladder. The proximity of the urethra to the vagina and anus also creates more opportunities for bacteria to enter the bladder.
• Anything that impedes the flow of urine or reduces your ability to completely empty your bladder when urinating, such as a kidney stone, structural abnormalities in your urinary system, or, in men, an enlarged prostate gland can increase your risk of kidney infection.
• Medical conditions that impair your immune system, such as cancer, diabetes or the human immunodeficiency virus (HIV), increase your risk of kidney infection. Certain medications, such as drugs taken to prevent rejection of transplanted organs, have a similar effect.
• Nerve or spinal cord damage may block the sensations of a bladder infection, allowing it to progress into the kidney.
• Prolonged catheterization: You may have a catheter placed in your bladder during and after some surgical procedures and diagnostic tests. A catheter may be used continuously if you are confined to a bed.
• People with vesicoureteral reflux (small amounts of urine flow from your bladder back up into your ureters and kidneys) are at higher risk of kidney infection during both childhood and adulthood.

Symptoms of Kidney Infection:
Kidney infections often cause urinary problems, such as the need to urinate more often, an inability to urinate, blood in the urine (hematuria), and pus in the urine. Infections also can cause changes in urine color or odor. Additional symptoms include bouts of back or abdominal pain.
Severe kidney infection may induce unexplained bouts of confusion / fatigue, fever, chills, night sweats, loss of appetite, and nausea. If these symptoms are present you should contact your doctor immediately.

Because the symptoms of kidney infections and other urinary tract infections (UTIs) are similar, kidney infections may be difficult to diagnose. Patients should contact their health care provider at the first sign of symptoms. Early detection and treatment of a UTI can decrease the likelihood that a kidney infection will develop: untreated kidney infections can cause blood poisoning, kidney scars, kidney disease, and permanent kidney damage. Kidney infections during pregnancy can result in premature labor and low birth weight.

Treatment of Kidney Infections:
If your symptoms are typical and you're in general good health, antibiotics are the first line of treatment for kidney infection. Which drugs you use and for how long depends on your health condition and the bacteria found in your urine tests. Drugs commonly recommended for treating kidney infection include Amoxicillin (Amoxil, Trimox), Quinolones such as ciprofloxacin (Cipro) and norfloxacin (Noroxin), and antibiotic combinations such as sulfamethoxazole and trimethoprim (Bactrim, Septra).
Symptoms of kidney infection usually begin to clear up within a few days of treatment, but you may need to continue antibiotics for a week or more.
Recurrent kidney infections may result from an underlying medical problem, such as a structural abnormality. Your doctor may refer you to a kidney specialist (nephrologist) or urinary surgeon (urologist) for an evaluation to determine if urologic abnormalities may be causing your infections. A structural abnormality may need to be surgically repaired.
For severe kidney infection, hospitalization and treatment with intravenous antibiotics may be necessary. When recurrences of kidney infection are frequent or the infection becomes chronic, your doctor will likely recommend that you seek medical care from a specialist who can identify underlying and potentially treatable causes.