Acute uncomplicated urinary tract infection (UTI) is one of the most common bacterial infections in adults that may involve the lower or upper urinary tract or both.
Acute cystitis is an infection limited to the lower urinary tract while acute pyelonephritis is an infection that involves the upper urinary tract (renal parenchyma & pelvicaliceal system) that usually has significant bacteriuria.
Recurrent UTI is characterized by 2 episodes of uncomplicated UTI in the last 6 months or ≥3 episodes with positive cultures in the last 12 months in patients with no structural or functional abnormalities.


  • One of the most common bacterial infections in adults that may involve the lower or upper urinary tract or both
    • Common in women without urinary tract functional or structural abnormalities, renal disease, or comorbidities
    • 70-95% of cases are caused by Escherichia coli; 5-10% are secondary to Staphylococcus saprophyticus, but enterobacteriaceae organisms or enterococci (Proteus mirabilis, Klebsiella sp) are occasionally isolate


Acute Cystitis

  • An infection limited to the lower urinary tract

Acute Pyelonephritis

  • An infection that involves the upper urinary tract (renal parenchyma and pelvicaliceal system) that usually has significant bacteriuria

Recurrent Urinary Tract Infection (UTI)

  • Characterized by 2 episodes of uncomplicated UTI in the last 6 months or ≥3 episodes with positive cultures in the last 12 months in patients with no structural or functional abnormalities
    • Considered as relapse if UTI is caused by the same organism after an adequate therapy was given and reinfection if UTI is caused by an organism that was previously isolated after treatment and a negative intervening urine culture result, or a UTI caused by another pathogen
    • Reinfection is more common than relapse
    • Recurrences usually occur within the 1st 3 months after initial infection

Complicated Urinary Tract Infection (UTI)

  • An infection in patients with structural or functional abnormality or with underlying disease that interferes with host defense mechanisms that increases the risks of acquiring infection or of failing therapy
    • Considered in patients with the following:
      • Obstruction (eg ureteric or urethral strictures, tumors, urolithiasis, prostatic hypertrophy, diverticulae, pelvicaliceal obstruction, renal cysts)
      • Instrumentation (eg indwelling catheter, intermittent catheterization, ureteric stent, nephrostomy tube, urological procedures)
      • Impaired voiding (eg neurogenic bladder, vesicoureteral reflux, ileal conduit)
      • Metabolic abnormalities (eg nephrocalcinosis, medullary sponge kidney, renal failure)
      • Post-void residual urine >100 mL
      • Peri- and post-operative UTI
      • Immunodeficiency (eg renal transplant, diabetes)
      • Pregnancy
    • Please see Urinary Tract Infection - Complicated Disease Management Chart for more details

Signs and Symptoms

Acute Cystitis

  • Clinical features include dysuria, urgency, frequency, suprapubic pain, and absence of urinary symptoms in the past 4 weeks
  • Presence of urinary irritative symptoms and absence of vaginal discharge or irritation and risk factors for complicated urinary tract infections (UTIs) increase the probability of acute uncomplicated cystitis in premenopausal nonpregnant women

Acute Pyelonephritis

  • Characterized by fever >38ºC, chills, flank pain, costovertebral tenderness, nausea and vomiting with or without symptoms of lower UTI (cystitis) with no history or clinical evidence of urological abnormalities

Risk Factors

  • Anatomical: Shorter urethra of females
  • Behavioral factors
    • Sexual activity, delayed postcoital micturition
      • A new sexual partner and increased frequency of intercourse may increase the risk of recurrent urinary tract infection (UTI)
    • Use of diaphragms and spermicides can promote colonization of the periurethral area with coliform bacteria and is a risk factor for recurrent UTI
  • Obstetric history: Increased risk in patients with increased parity
  • History of recent UTI, urinary calculi, genitourinary instrumentation, surgery and congenital defects
    • Risk of a 2nd UTI within 6 months is higher when the 1st infection is caused by E coli
  • Presence of comorbidities (eg DM, obesity, sickle cell trait)
  • Postmenopausal women
    • At increased risk for recurrent UTI due to decrease in vaginal estrogen, vaginal atrophy, urinary incontinence, cystocele, rectocele, urethrocele, uterovaginal prolapse, incomplete bladder emptying, ABO blood group nonsecretor status, history of UTI, vaginal atrophy, poor perineal hygiene in elderly institutionalized women 
  • Recurrent UTI may be common in patients who had their 1st episode of infection at age <15 years old and maternal history of UTI
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