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Pyelonephritis, Acute

Causes

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 often in females, probably because of a shorter urethra and the proximity of the urinary meatus to the vagina and the rectum (both of which allow bacteria to reach the bladder more easily) and a lack of the antibacterial prostatic secretions produced in the male.

Risk factors

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 pyelonephritis.
• diabetics - neurogenic bladder causes incomplete emptying and urinary stasis; glycosuria may support bacterial growth in the urine.
• people with other renal diseases­increased susceptibility resulting from compromised renal function.

Signs and symptoms

Typical clinical features include urgency, frequency, burning during urination, dysuria, nocturia, and hematuria (usually microscopic but may be gross). Urine may appear cloudy and have an ammoniacal or fishy odor. Other common symptoms include a temperature of 102° F (38.9° C) or higher, shaking chills, flank pain, anorexia, and general fatigue.

These symptoms characteristically develop rapidly over a few hours or a few days. Although these symptoms may disappear within days, even without treatment, residual bacterial infection is likely and may cause later recurrence of symptoms.

Diagnosis

Diagnosis requires urinalysis and culture. Typical findings include

• pyuria (pus in urine)-urine sediment reveals the presence of leukocytes singly, in clumps, and in casts; and, possibly, a few red blood cells
• significant bacteriuria - more than 100,000 organisms/µ1 of urine revealed in urine culture
• low specific gravity and osmolality­resulting from a temporarily decreased ability to concentrate urine
• slightly alkaline urine pH
• proteinuria, glycosuria, and ketonuria -less common.

X-rays also help in the evaluation of acute pyelonephritis. X-rays of the kidneys-ureters-bladder may reveal calculi, tumors, or cysts in the kidneys and the urinary tract. Excretory urography may show asymmetrical kidneys.

Treatment

Effective treatment centers on antibiotic therapy appropriate to the specific infecting organism after identification by urine culture and sensitivity studies.

Antibiotic therapy

S. faecalis requires treatment with ampicillin, penicillin G, or vancomycin. S. aureus requires penicillin G or, if resistance develops, a semisynthetic penicillin, such as nafcillin, or a cephalosporin. E. coli may be treated with sulfisoxazole, nalidixic acid, and nitrofurantoin; Proteus, with ampicillin, sulfisoxazole, nalidixic acid, and a cephalosporin; and Pseudomonas, with gentamicin, tobramycin, and carbenicillin.

When the infecting organism can't be identified, therapy usually consists of a broad-spectrum antibiotic, such as ampicillin or cephalexin. If the patient
is pregnant, antibiotics must be prescribed cautiously. Urinary analgesics such as phenazopyridine are also appropriate.

Symptoms may disappear after several days of antibiotic therapy. Although urine usually becomes sterile within 48 to 72 hours, the course of such therapy is 10 to 14 days.

Follow-up treatment

Follow-up treatment includes reculturing urine 1 week after drug therapy stops, then periodically for the next year to detect residual or recurring infection. Most patients with uncomplicated infections respond well to therapy and don't suffer re-infection.

Prevention

Persons with a history of urinary tract infections should urinate frequently, and drink plenty of fluids at the first sign of infection. Women should void after intercourse which may help flush bacteria from the bladder. Girls should be taught to wipe their genital area from front to back after urinating to avoid getting fecal matter into the opening of the urinary tract.