Description

• A syndrome caused by infection of the renal parenchyma and/or renal pelvis, often producing localized flank/back pain combined with systemic symptoms, such as fever, chills, nausea and vomiting; there is a wide spectrum of illness ranging from mild symptoms to septic shock.
• Chronic pyelonephritis is the result of progressive inflammation of the renal interstitium and tubules, due to recurrent infection, vesicoureteral reflux, or both.
• Pyelonephritis is considered uncomplicated if the infection is caused by a typical pathogen in an immunocompetent patient with normal urinary tract anatomy and renal function.

Geriatric Considerations
May present as altered mental status; absence of fever is common in older adults. Older patients with diabetes and pyelonephritis are at higher risk of bacteremia, prolonged hospitalization, and mortality. The high prevalence of asymptomatic bacteriuria (ABU) in older adults makes the use of urine dipstick less reliable for diagnosing UTI in this population. Culture and sensitivity data are more useful in guiding antimicrobial therapy for pyelonephritis in older adults and should therefore be obtained.

Pregnancy Considerations
Most common medical complication requiring hospitalization; pregnant patients with ABU have 20–30% risk to develop acute pyelonephritis if ABU is not treated. Affects 1–2% of all pregnancies; morbidity does not differ between trimesters. Urine culture for test of cure 1 to 2 weeks after therapy; consider low-dose suppressive antibiotics for the remainder of pregnancy following treatment for pyelonephritis or recurrent cystitis in pregnancy.

Pediatric Considerations
UTI is present in ~5% of patients aged 2 months to 2 years with fever and no apparent source on history and physical exam. Treatment (PO or IV; inpatient or outpatient) should be based on the clinical situation and patient toxicity.

Epidemiology

Incidence
Community-acquired acute pyelonephritis: 3 to 4 cases per 10,000 males; 15 to 17 cases per 10,000 females; 28 cases per 10,000 women aged 18 to 49 years

Prevalence
Adult cases: 250,000/year, with 200,000 hospitalizations

Etiology and Pathophysiology

• Escherichia coli (>80%); other gram-negative pathogens: Proteus, Klebsiella, Serratia, Clostridium, Pseudomonas, and Enterobacter spp.; Enterococcus spp.
• Staphylococcus: Staphylococcus epidermidis, Staphylococcus saprophyticus (number 2 cause in young women), and Staphylococcus aureus; Candida spp.

Risk Factors

• Underlying urinary tract abnormalities; indwelling catheter/recent urinary tract instrumentation; nephrolithiasis; immunocompromised, including diabetes; elderly, institutionalized patients (particularly women); prostatic enlargement, stress incontinence
• Childhood UTI; acute pyelonephritis within the prior year; recent sexual intercourse; spermicide use; new sex partner within the prior year; pregnancy; hospital-acquired infection; symptoms >7 days at time of presentation

Commonly Associated Conditions

• Indwelling catheters, renal calculi
• Benign prostatic hyperplasia