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One of the most common renal diseases, acute pyelonephritis (also known as acute infective tubulointerstitial nephritis) is a sudden inflammation caused by bacteria that primarily affects the interstitial area and the renal pelvis or, less often, the renal tubules. With treatment and continued follow-up, the prognosis is good and extensive permanent damage is rare. (See Chronic pyelonephritis.)
Acute pyelonephritis results from bacterial infection of the kidneys. Infecting bacteria usually are normal intestinal and fecal flora that grow readily in urine. The most common causative organism is Escherichia coli, but Proteus, Pseudomonas, Staphylococcus aureus, and Streptococcus faecalis may also cause such infections.
Typically, the infection spreads from the bladder to the ureters, then to the kidneys, as in vesicoureteral reflux. Vesicoureteral reflux may result from congenital weakness at the junction of the ureter and the bladder.
Bacteria refluxed to intrarenal tissues may create colonies of infection within 24 to 48 hours. Infection may also result from instrumentation (such as catheterization, cystoscopy, or urologic surgery), from a hematogenic infection (as in septicemia or endocarditis) or, possibly, from lymphatic infection.
Pyelonephritis may also result from an inability to empty the bladder (for example, in patients with neurogenic bladder), urinary stasis, or urinary obstruction due to tumors, strictures, or benign prostatic hyperplasia.
Pyelonephritis occurs more commonly in females, probably because of a shorter urethra and the proximity of the urinary meatus to the vagina and rectum (both of which allow bacteria to reach the bladder more easily) and a lack of the antibacterial prostatic secretions produced in the male.
Incidence increases with age and is higher in the following groups:
sexually active women—increased risk of bacterial contamination from intercourse.
pregnant women—about 5% develop asymptomatic bacteriuria; if untreated, about 40% develop pyelo-nephritis.
diabetics—neurogenic bladder causes incomplete emptying and urinary stasis; glycosuria may support bacterial growth in the urine.
people with other renal diseases—increased susceptibility resulting from compromised renal function.
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