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Acute pyelonephritis is a syndrome caused by an infection of the renal parenchyma and renal pelvis, often producing localized flank/back pain combined with systemic symptoms, such as fever, chills, and nausea. It has a wide spectrum of presentation, from mild illness 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 who has normal urinary tract anatomy and renal function.
System(s) affected: renal; urologic
Synonym: acute upper urinary tract infection (UTI)
May present as altered mental status; absence of fever is common in this age group.
Elderly patients with diabetes and pyelonephritis are at higher risk of bacteremia, longer hospitalization, and mortality.
The high prevalence of asymptomatic bacteriuria in the elderly makes the use of urine dipstick less reliable for diagnosing UTI in this population 1[A].
Most common medical complication requiring hospitalization
Affects 1-2% of all pregnancies. Morbidity does not differ between trimesters.
Urine culture as test of cure 1 to 2 weeks after therapy
UTI is present in ~5% of patients age 2 months to 2 years with fever and no apparent source on history and physical exam.
Treatment (oral or IV; inpatient or outpatient) should be based on the clinical situation and patient toxicity.
Escherichia coli (>80%)
Other gram-negative pathogens: Proteus, Klebsiella, Serratia, Clostridium, Pseudomonas, and Enterobacter
Staphylococcus: Staphylococcus epidermis, Staphylococcussaprophyticus (number 2 cause in young women), and Staphylococcus aureus
Underlying urinary tract abnormalities
Indwelling catheter/recent urinary tract instrumentation
Immunocompromise, including diabetes
Elderly, institutionalized patients (particularly women)
Acute pyelonephritis within the prior year
Frequency of recent sexual intercourse; spermicide use; new sex partner within the prior year
Stress incontinence in the previous 30 days
Symptoms >7 days at time of presentation
Benign prostatic hyperplasia
In infants and children
Acute bacterial pneumonia (lower lobe)
Perforated viscus; aortic dissection
Pelvic inflammatory disease; ectopic pregnancy
Urinalysis: pyuria ± leukocyte casts, hematuria, nitrites (sensitivity 35-85%; specificity 92-100%), and mild proteinuria
Urine leukocyte esterase positive (sensitivity 74-96%; specificity 94-98%)
Urine Gram stain; urine culture (>100,000 colony-forming units/mL or >100 colony forming units/mL + symptoms) and sensitivities
CBC, BUN, Cr, GFR, and pregnancy test (if indicated)
C-reactive protein levels have been shown to correlate with prolonged hospitalization and recurrence; serum albumin ≪3.3 g/dL also associated with risk for hospital admission.
Imaging not necessary in routine cases
Pediatrics: Recent guidelines recommend renal/bladder US (not voiding cystourethrogram), after first UTI.
Catheterization/suprapubic aspirate should be used to obtain samples from non-toilet-trained children.
Catheterization may also be necessary for some geriatric patients.
Blood culture(s): indicated if diagnostic uncertainty, immunosuppression, or a suspected hematogenous source
Recent antibiotic use may alter lab results.
If patient’s condition does not improve within 72 hours, if obstruction/anatomic abnormality suspected, or if certain lab abnormalities are present (urine pH >7, GFR ≪40, 50% decline in renal function), consider:
Acute: abscess formation with neutrophil response
Chronic: fibrosis with reduction in renal tissue
≤7 days of treatment is equivalent to longer regimens in adults (including those with bacteremia) without urogenital abnormalities 2[A].
IV antibiotics are indicated for inpatients who are toxic appearing or unable to tolerate oral antibiotics.
Broad-spectrum antibiotics initially, tailor therapy to culture and sensitivity results
Analgesics and antipyretics
Consider urinary analgesics (e.g., phenazopyridine 200 mg q8h) for dysuria.
For empiric oral therapy, a fluoroquinolone is recommended. Should fluoroquinolone resistance exceed 10% or the patient has nausea/vomiting, a single initial IV dose of a long-acting antibiotic such as ceftriaxone 1 g is additionally recommended.
For parenteral therapy, fluoroquinolone, aminoglycoside ± ampicillin, an extended-spectrum cephalosporin with or without a β-lactamase inhibitor, an extended-spectrum penicillin with or without an aminoglycoside, or a carbapenem are recommended.
Treat children ≪2 years of age and children with febrile or recurrent UTI for 10 to 14 days.
Initial empiric antibiotic choice should cover E. coli. Add ampicillin if Enterococcus is suspected.
Complete outpatient antibiotic course in entirety
Acute pyelonephritis unresponsive to therapy
Abnormal urogenital anatomy
Inpatient therapy for severe illness (e.g., high fevers, severe pain, marked debility, intractable vomiting, inability to tolerate oral intake, possible sepsis), risk factors for complicated pyelonephritis, pregnancy, or extremes of age
Outpatient therapy if mild to moderate illness (not pregnant, no nausea/vomiting; fever and pain not severe), uncomplicated, and tolerating oral hydration and medications. Many patients can be treated as outpatients.
IV fluids as indicated for dehydration or renal calculi
Discharge on oral agent after patient is afebrile 24 to 48 hours to complete up to 2 weeks of therapy.
Women: Routine follow-up cultures not recommended unless symptoms recur after 2 weeks; then, urologic evaluation is necessary.
Men, children, adolescents, patients with recurrent infections, patients with risk factors: repeat cultures 1 to 2 weeks after completing therapy; urologic evaluation after first episode of pyelonephritis and with recurrences
No response within 48 hours (5% of patients): Reevaluate and review cultures, CT scan, or US to review anatomy; adjust therapy as needed; urologic consult. The two most common causes of failure to respond are a resistant organism and nephrolithiasis.
Work with parents to monitor response in children.
Metastatic infection: skeletal system, endocardium, eye, meningitis with subsequent seizures
Septic shock and death
Acute/chronic renal failure
Beetz R, Westenfelder M. Antimicrobial therapy of urinary tract infections in children. Int J Antimicrob Agents. 2011;38(Suppl):42–50.
Goel RH, Unnikrishnan R, Remer EM. Acute urinary tract disorders. Radiol Clin N Am. 2015;53(6):1273–1292.
Gupta K, Hooton TM, Naber KG, et al. International clinical practice guidelines for the treatment of acute uncomplicated cystitis and pyelonephritis in women: a 2010 update by the Infectious Diseases Society of America and the European Society for Microbiology and Infectious Diseases. Clin Infect Dis. 2011;52(5):e103–e120.
Noelle L. Urinary tract infections in older adults. Clin Geri Med. 2016;32:532–538.
Roberts KB; and the Subcommittee on Urinary Tract Infection, Steering Committee on Quality Improvement and Management. Urinary tract infection: clinical practice guideline for the diagnosis and management of the initial UTI in febrile infants and children 2 to 24 months. Pediatrics. 2011;128(3):595–610.
Takhar SS, Moran GJ. Diagnosis and management of urinary tract infection in the emergency department and outpatient settings. Infect Dis Clin North Am. 2014;28(1):33–48.
Wagenlehner FM, Umeh O, Steenbergen J, et al. Ceftolazone-tazobactam compared to levofloxacin in treatment of complicated urinary tract infections, including pyelonephritis: a randomized, double-blind, phase 3 trial (ASPECT-cUTI). Lancet. 2015;385(9981):1949–1956.
Wang A, Nizran P, Malone MA, et al. Urinary tract infections. Prim Care. 2013;40(3):687–706.
N12 Tubulo-interstitial nephritis, not spcf as acute or chronic
N10 Acute tubulo-interstitial nephritis
N11.9 Chronic tubulo-interstitial nephritis, unspecified
N11.8 Other chronic tubulo-interstitial nephritis
N11.1 Chronic obstructive pyelonephritis
590.80 Pyelonephritis, unspecified
590.10 Acute pyelonephritis without lesion of renal medullary necrosis
590.00 Chronic pyelonephritis without lesion of renal medullary necrosis
590.11 Acute pyelonephritis with lesion of renal medullary necrosis
590.01 Chronic pyelonephritis with lesion of renal medullary necrosis
45816000 Pyelonephritis (disorder)
197768004 Acute pyelonephritis without medullary necrosis (disorder)
197760006 Chronic pyelonephritis without medullary necrosis (disorder)
197769007 Acute pyelonephritis with medullary necrosis (disorder)
197761005 Chronic pyelonephritis with medullary necrosis (disorder)
Pyelonephritis can present with isolated confusion or mental status changes (no fever) in the elderly.
The most common causes of poor response to treatment are antibiotic resistance and coexisting nephrolithiasis.
Fluoroquinolones are generally the initial drugs of choice for treating pyelonephritis. Oral β-lactams are less effective, with the exception that parental β-lactams may be preferred in cases of complicated urinary tract infections.