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Pyelonephritis

BASICS

  • Definition: Infection of renal parenchyma and/or pelvis, causing localized flank/back pain and systemic symptoms (fever, chills, nausea, vomiting). Severity ranges from mild to septic shock.
  • Chronic pyelonephritis: Progressive renal inflammation due to recurrent infection, vesicoureteral reflux, or both.
  • Uncomplicated pyelonephritis: Typical pathogen, immunocompetent, normal urinary tract and renal function.

Special Populations

  • Geriatrics: Often presents with altered mental status; fever may be absent. High risk of bacteremia/mortality in diabetics. Use culture/sensitivity to guide therapy.
  • Pregnancy: 1-2% affected. Most common cause of medical hospitalization. Untreated ABU can progress to pyelonephritis. Increased risk of ARDS, preterm labor.
  • Pediatrics: ˜5% of 2 months–2 years old with fever and no clear source. Use catheter/suprapubic aspiration for UA.

EPIDEMIOLOGY

  • Incidence:
  • 3–4/10,000 males
  • 15–17/10,000 females
  • 28/10,000 women aged 18–49
  • Prevalence: 250,000 adult cases/year; 200,000 hospitalizations/year

ETIOLOGY & PATHOPHYSIOLOGY

  • Pathogens:
  • E. coli (>80%)
  • Proteus, Klebsiella, Serratia, Clostridium, Pseudomonas, Enterobacter spp.
  • Enterococcus spp., Staphylococcus saprophyticus (young women)
  • Candida spp. (rare)

RISK FACTORS

  • Urinary tract abnormalities
  • Indwelling catheter, recent instrumentation
  • Nephrolithiasis
  • Immunocompromised, diabetes, elderly
  • BPH, stress incontinence, recurrent childhood UTI, recent sexual activity, spermicide use, new sexual partner, pregnancy, hospital-acquired infection, symptoms >7 days

COMMON ASSOCIATED CONDITIONS

  • Indwelling catheters
  • Renal calculi
  • Benign prostatic hyperplasia

DIAGNOSIS

History

  • Adults: Fever, flank pain, nausea/vomiting, malaise, dysuria, urgency, suprapubic discomfort, altered mental status (elderly)
  • Children: Fever, irritability, poor feeding, GI symptoms

Physical Exam

  • Adults: May range from afebrile to septic shock; fever β‰₯38Β°C; CVA tenderness; altered mental status.
  • Infants/children: Lethargy, fever, pallor, poor skin perfusion, jaundice.

Differential Diagnosis

  • Obstructive uropathy, pneumonia, cholecystitis, pancreatitis, appendicitis, perforated viscus, PID, ectopic pregnancy, kidney stone, diverticulitis

Diagnostic Tests

  • Urinalysis: Pyuria (>5 WBC/HPF), leukocyte casts, hematuria, nitrites, mild proteinuria, leukocyte esterase positive
  • Urine culture: >100,000 CFU/mL or >100 CFU/mL + symptoms
  • CBC, BUN, creatinine, GFR, pregnancy test
  • CRP: Higher levels correlate with longer hospital stay/recurrence; albumin <3.3 g/dL increases risk
  • Imaging: Usually not needed unless poor response at 72h, suspicion of obstruction/anatomy, severe comorbidity. CECT preferred. Renal/bladder US for 2–24 months old with first febrile UTI.
  • Pediatrics: Urine by catheter/suprapubic aspirate. Blood cultures if hospitalized or severe.

TREATMENT

General Principles

  • ≀7 days of antibiotics is as effective as longer courses in adults without urogenital abnormalities.
  • Obtain urine cultures before starting antibiotics.
  • Broad-spectrum empiric antibiotics, then tailor to sensitivities.

First Line Antibiotics

  • Adults (Outpatient Oral):
  • Ciprofloxacin 500 mg q12h or XR 1000 mg q24h (5–7 days)
  • Levofloxacin 750 mg q24h (5–7 days)
  • TMP-SMX 160/800 mg q12h (10–14 days; if susceptible)
  • Initial single-dose ceftriaxone 1g IV/IM if fluoroquinolone resistance >10% or patient can’t tolerate PO
  • Adults (Inpatient IV):
  • Ciprofloxacin 400 mg q12h, levofloxacin 750 mg q24h
  • Cefotaxime 1–2 g q8–12h, ceftriaxone 1–2 g/day, cefepime 1–2 g q12h
  • Gentamicin 5–7 mg/kg q24h
  • Piperacillin-tazobactam 3.375 g q6–8h
  • Ampicillin 2g q6h Β± gentamicin for Enterococcus

  • MDR risk: Use carbapenem (meropenem 1g q8h, imipenem 500 mg q6h), add vancomycin for MRSA or daptomycin/linezolid for VRE

  • Pediatric:

  • Oral: cefdinir, ceftibuten, cefixime

  • IV: ceftriaxone, cefotaxime, ampicillin + gentamicin (doses by weight/age)

  • Pregnancy:

  • Aggressive IV cephalosporin therapy; consider low-dose suppressive antibiotics for remainder of pregnancy after treatment

Second Line

  • Oral Ξ²-lactams (e.g., cefpodoxime, amoxicillin-clavulanate) for 10–14 days (less effective)

Other Measures

  • Urinary analgesics: Phenazopyridine 200 mg q8h for dysuria
  • Monitor renal function; adjust dose as needed
  • Hospitalize if severe, immunocompromised, unable to tolerate PO, pregnant, or <2 months old

Duration

  • Adults and children: Follow up 48–72h; outpatient therapy if stable and improving.
  • Severe illness: IV until afebrile 24–48h, then switch to PO to complete up to 2-week course.
  • Children <2 years or febrile/recurrent UTI: 10–14 days of therapy

ONGOING CARE & MONITORING

  • Follow up at 48–72h for outpatients
  • Repeat urine culture only for complicated cases or non-response
  • If no improvement in 48–72h: Review cultures, imaging, consider nephrolithiasis/resistance, consult urology/ID

DIET

  • Encourage increased fluid intake

PROGNOSIS

  • 95% respond to treatment within 48h

COMPLICATIONS

  • Renal abscess, perinephric abscess
  • Metastatic infection (bone, endocardium, eye, meningitis)
  • Septic shock, death
  • Acute/chronic renal failure

ICD-10 Codes

  • N12 Tubulo-interstitial nephritis, not specified as acute or chronic
  • N10 Acute tubulo-interstitial nephritis
  • N11.9 Chronic tubulo-interstitial nephritis, unspecified

CLINICAL PEARLS

  • Urine culture is key for targeted therapy.
  • Most common causes of poor response: antibiotic resistance and nephrolithiasis.
  • Fluoroquinolones are initial antibiotic of choice; oral Ξ²-lactams are less effective.
  • Parenteral Ξ²-lactams are reserved for complicated UTIs.