Urinary Tract Infection

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
Microbe	Findings	Comments
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	Large mucoid capsule and viscous colonies	Third most common cause
S. marcescens	Red pigment production by select strains	–
Enterococcus	–	Typically a nosocomial infection that is drug-resistant
P. mirabilis	“Swarming” appearance on agarUrease positiveCan result in struvite 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