Risk factors

Factors that increase your risk of a kidney infection include:

• Being female. The urethra is shorter in women than it is in men, which makes it easier for bacteria to travel from outside the body to the bladder. The nearness of the urethra to the vagina and anus also creates more opportunities for bacteria to enter the bladder.

  Once in the bladder, an infection can spread to the kidneys. Pregnant women are at even higher risk of a kidney infection.

• Having a urinary tract blockage. This includes anything that slows the flow of urine or reduces your ability to empty your bladder when urinating — including a kidney stone, something abnormal in your urinary tract's structure or, in men, an enlarged prostate gland.
• Having a weakened immune system. This includes medical conditions that impair your immune system, such as diabetes and HIV. Certain medications, such as drugs taken to prevent rejection of transplanted organs, have a similar effect.
• Having damage to nerves around the bladder. Nerve or spinal cord damage can block the sensations of a bladder infection so that you're unaware when it's advancing to a kidney infection.
• Using a urinary catheter for a time. Urinary catheters are tubes used to drain urine from the bladder. You might have a catheter placed during and after some surgical procedures and diagnostic tests. You might use one continuously if you're confined to a bed.
• Having a condition that causes urine to flow the wrong way. In vesicoureteral reflux, small amounts of urine flow from your bladder back up into your ureters and kidneys. People with this condition are at higher risk of kidney infection during childhood and adulthood.