Updated: 10/7/2022

Urinary Tract Infection

Review Topic
  • Snapshot
    • A 23-year-old woman presents to her primary care physician due to pain with urination and increased urinary frequency. She reports that her symptoms began approximately 3 days ago and has not noticed any abnormal smell, vaginal discomfort, or vaginal discharge. The patient is otherwise healthy and states that she has been having sexual intercourse more frequently with her partner. She infrequently uses condoms and is on oral contraception. Her vital signs and physical examination is unremarkable. She is started on oral nitrofurantoin for 5 days. (Acute uncomplicated cystitis)
  • Introduction
    • Clinical definitionurinary tract infections (UTI) can either be asymptomatic or symptomatic and encompasses
        • asymptomatic bacturia (ASB)
          • there is bacteria in the urinary tract; however, the patient has no symptoms
          • typically patients do not require treatment
            • pregnant women require screening and treatment
              • this is because ASB in pregnancy is associated with
                • pre-term birth
                • perinatal death
                • pyelonephritis in the mother
        • cystitis
        • prostatitis
        • pyelonephritis
          • neutrophillic infiltration of the interstitium and tubular lumen on histology
      • it is important to distinguish between uncomplicated versus complicated UTI
        • uncomplicated UTI
          • this describes acute cystitis or pyelonephritis in outpatient women who are not pregnant and do not have anatomic abnormalities or instrumentation within the urinary tract
        • complicated UTI
          • this describes UTI that is not uncomplicated
    • Epidemiology
      • incidence
        • 50-80% of women acquire at least 1 UTI
        • 20-30% of women with 1 UTI have recurrent infections
      • demographics
        • more common in women, elderly, and infants
      • location
        • bladder
        • prostate
        • kidneys
      • risk factors
        • female
        • benign prostatic hyperplasia
        • frequent sexual intercourse
        • history of UTI
        • incontinence
        • diabetes mellitus
        • vasicoureteral reflux
        • spermicide use
        • prolonged catheterization (most important for catheter associated UTI)
    • Pathogenesis
      • in most cases bacteria ascends from the urethra to the bladder (cystitis)
        • bacterial organisms can further ascend through the ureter and infect the kidney causing a renal parenchymal infection (pyelonephritis)
        • note that infection and symptom development depends on the
          • host
            • e.g., genetic background, behavioral factors, and underlying disease
          • pathogen
          • environmental factors
            • e.g., vaginal microflora, medical devices (e.g., indwelling catheters), and urinary retention
          • for example, voiding and the host's innate immune response eliminates bacterial colonization in the bladder after sexual intercourse
            • however, an indwelling catheter, stone, or any other foreign body provides a surface where bacteria can colonize
        • hematogenous spread to the urinary tract can also result in a UTI; however, this is rare
          • e.g., Salmonella, S. aureus, and Candida
    • Prognosis
      • ASB in elderly or catheterized patients does not increase the risk of death
      • recurrent UTI in children and adults does not result in chronic pyelonephritis or renal failure
        • this is true when there are not anatomic abnormalities
    • Microbiology of Urinary Tract Infections
      E. coli
      • Green metallic sheen on EMB agar
      • Most common cause of UTI
      S. saprophyticus
      • Second most common cause in sexually active women
      K. pneumoniae
      • Largemucoid capsule and viscous colonies
      • Third most common cause
      S. marcescens
      • Red pigment production by select strains
      • Typically a nosocomial infection that is drug-resistant
      P. mirabilis
      • "Swarming"appearance on agar
      • Urease positive
      • Can result instruvite stone formation
      P. aeruginosa
      • Blue-green pigment
      • Typically a nosocomial infection that is drug-resistant
  • Presentation
    • Symptoms/physical exam/findings
      • ASB
        • asymptomatic patient with an incidental finding of bacteruria on urine culture
      • cystitis
        • dysuria
        • urinary frequency
        • urgency
        • nocturia
        • suprapubic discomfort
        • gross hematuria
      • prostatitis
        • dysuria
        • frequency
        • pain in the prostatic pelvic or perineal area
        • bladder outlet obstruction
        • fever and chills
      • pyelonephritis
        • fever
          • this is the main feature that distinguishes pyelonephritis from cystitis
        • costovertebral angle pain
          • may be absent in mild pyelonephritis
        • obstructive uropathy in patients with diabetes
          • this is secondary to acute papillary necrosis that results in the papillae to slough and subsequently obstruct the ureter
        • emphysematous pyelonephritis in patients with diabetes
          • gas is produced in the renal and perinephric areas
  • Studies
    • Labs
      • urine dipstick
        • nitrite positivity suggests an E. coli infection or other infection of the Enterobacteriaceae family
        • leukocyte esterase positive
        • urease positivity suggests an S. saprophyticus, Proteus, or Klebsiella infection
      • urinalysis
        • > 10 white blood cells (WBCs)/mL
        • > 1000 CFU/mL
        • white blood cell casts
          • a diagnostic finding of an upper urinary tract infection (e.g., pyelonephritis)
      • urine culture
        • gold standard for diagnosing UTI
        • may appear sterile if caused by chlamydia
          • most common cause of sterile pyuria in sexually active males age 20-30
    • Histology
      • chronic pyelonephritis
        • "thyroidization" of tubules due to eosinophilic casts contained in the tubules
  • Differential
    • Acute hemorrhagic cystitis
      • can be caused by adenovirus
    • Urethritis
    • Nephrolithiasis
    • Genitourinary malignancy
  • Treatment
    • Medical
      • TMP-SMX or nitrofurantoin
        • indications
          • first-line for uncomplicated UTI
            • second-line agents include a fluoroquinolone or β-lactam
          • nitrofurantoin, ampicillin, and cephalosporins can be used in the treatment of UTI in pregnant women
            • sulfonamides should not be used due to its possible teratogenic effects (in first trimester) and kernicterus development (near term)
            • fluoroquinolones should also be avoided in pregnancy due to its negative effect on the development of fetal cartilage
          • TMP-SMX or a fluoroquinolone is used in the treatment of prostatitis
      • fluoroquinolones (e.g., ciprofloxacin)
        • indication
          • first-line for acute uncomplicated pyelonephritis
      • fluconazole
        • indication
          • first-line treatment for Candida-related UTI
    • Operative
      • nephrectomy
        • indications
          • treatment for xanthogranulomatous pyelonephritis
      • percutaneous drainage
        • indications
          • treatment for emphysematous pyelonephritis and it may be followed by elective nephrectomy
  • Complications
    • Uncomplicated UTI
      • complications are uncommon
    • Complicated UTI
      • bacteremia
      • urosepsis
      • systemic inflammatory response syndrome (SIRS)
      • renal and perinephric abscess
      • emphysematous pyelonephritis
      • xanthogranulomatous pyelonephritis
        • associated with long-term urinary tract obstruction and infection
          • this results in chronic destruction of the renal parenchyma via a granulomatous process
      • malakoplakia
      • renal papillary necrosis
    • UTI in pregnancy
      • pyelonephritis
      • sepsis
      • chorioamnionitis
      • preterm labor
      • low birth weight
      • hypertension and pre-eclampsia
    • UTI in men
      • acute or chronic prostatitis
      • urethritis
      • acute epididymitis
      • orchitis
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(M1.RL.17.4756) A 4-year-old male is accompanied by his mother to the pediatrician. His mother reports that over the past two weeks, the child has had intermittent low grade fevers and has been more lethargic than usual. The child’s past medical history is notable for myelomeningocele complicated by lower extremity weakness as well as bowel and bladder dysfunction. He has been hospitalized multiple times at an outside facility for recurrent urinary tract infections. The child is in the 15th percentile for both height and weight. His temperature is 100.7°F (38.2°C), blood pressure is 115/70 mmHg, pulse is 115/min, and respirations are 20/min. Physical examination is notable for costovertebral angle tenderness that is worse on the right. Which of the following would most likely be found on biopsy of this patient’s kidney?

QID: 108920

Mononuclear and eosinophilic infiltrate



Replacement of renal parenchyma with foamy histiocytes



Destruction of the proximal tubule and medullary thick ascending limb



Diffusely necrotic papillae with dystrophic calcification



Tubular colloid casts with diffuse lymphoplasmacytic infiltrate



M 2 C

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(M1.RL.15.4671) A 22-year-old sexually active, otherwise healthy female presents to her primary care physician complaining of several days of dysuria, frequency, urgency, and suprapubic pain. She denies fever, flank pain, vaginal itching, or vaginal bleeding/discharge. Which organism is most likely responsible for this patient's symptoms?

QID: 107151

Staphylococcus saprophyticus



Chlamydia trachomatis



Proteus mirabilis



Klebsiella pneumoniae



Escherichia coli



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(M1.RL.15.4671) A 34-year-old female presents to her primary care physician with complaints of fevers, nausea/vomiting, and severe left flank pain that has developed over the past several hours. She denies any prior episodes similar to her current presentation. Physical examination is significant for a body temperature of 39.1 C and costovertebral angle tenderness. A urinalysis and urine microscopy are ordered. Which of the following findings on kidney histology would be expected in this patient?

QID: 107161

Interstitial fibrosis and lymphocytic infiltrate



Neutrophils filling the lumens of the renal tubules



Thickening of the capillaries and glomerular basement membrane



Scarring of the glomeruli



Enlarged, hypercellular glomeruli with 'wire-looping' of capillaries



M 2 D

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(M1.RL.13.49) A 33-year-old female presents with recent onset of painful urination, fever, and right flank pain. Urinary sediment analysis is positive for the presence of white blood cell casts and Gram-negative bacteria. She has not recently started any new medications. What is the most likely diagnosis in this patient?

QID: 101267

Pelvic Inflammatory Disease



Acute Interstitial Nephritis












M 2 E

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