• Clinical science

Urinary tract infections


Urinary tract infections (UTIs) are classified based on location as upper or lower UTIs, and based on presentation as complicated or uncomplicated. In particular, infection of the bladder is known as cystitis. UTIs are most commonly caused by Enterobacteriaceae, especially Escherichia coli. Women are at high risk of contracting UTIs due to a shorter urethra and the proximity of the anal and genital regions. Other risk factors include sexual intercourse, indwelling urinary catheters, pregnancy, and abnormalities of the urinary tract. Patients present with suprapubic pain, dysuria, urinary urgency and frequency. In typical presentations, clinical diagnosis is often possible and can be supported with findings of pyuria on urinalysis or positive leukocyte esterase and nitrites on a urine dipstick test. Further evaluation with urine culture and/or imaging may be required for patients with complicated cystitis. First-line empiric treatment options for uncomplicated cystitis include trimethoprim-sulfamethoxazole, nitrofurantoin, and fosfomycin. Pregnant women with cystitis should be screened and treated for asymptomatic bacteriuria.



Predisposing factors





Uncomplicated UTI

Immunocompetent, premenopausal women that are neither pregnant nor have any condition that predisposes them to an increased risk of infection or failed therapy (see list below)

Complicated UTI

Any condition or comorbidity that may predispose a patient to an increased risk of infection or failed therapy such as:

Recurrent UTI

≥ 2 infections/6 months


≥ 3 infections/year

Nosocomial urinary tract infection


Clinical features

  • Dysuria, frequency, urgency
  • Suprapubic pain
  • Gross hematuria may be present

Fever is usually absent in lower UTIs; therefore, fever and flank pain should be taken as a sign of more serious infection, such as pyelonephritis.




  • Clinical diagnosis in healthy women with a typical presentation
  • In patients with an atypical presentation, urinalysis is the most important diagnostic test for cystitis.

Laboratory tests

Dipstick urine test

  • Best initial test
  • Findings indicative of UTI

Urinalysis with microscopy

  • Confirmatory test
  • Required in children and adolescents
  • Clean-catch midstream specimen is necessary to avoid contamination with vaginal or skin flora. Straight catheterization of the bladder or suprapubic aspiration can also be performed if a clean catch cannot be obtained without contamination (e.g., in children who are not toilet trained.)
  • Diagnostic criteria for UTI
    • Pyuria: ≥5-10 WBC/high power field (hpf)
    • Bacteriuria: presence of bacteria on Gram stain (most commonly, gram-negative rods)
  • Leukocyte casts should be absent in lower UTIs.

Urine culture

  • Diagnostic criteria for UTI
  • Indications
    • Patients with the following characteristics or risk factors:
    • Suspected cystitis with the following characteristics:

Diagnostic imaging


Differential diagnoses

Interstitial cystitis (painful bladder syndrome)

  • Description: rare, chronic, noninfectious cystitis with an unknown etiology; that causes suprapubic pain and scarring of the bladder wall
  • Clinical findings
    • Suprapubic pain or discomfort
      • Relieved by voiding and worsened by bladder filling (most common feature)
      • Other exacerbating factors include sexual activity, exercise, alcohol use, and prolonged sitting
    • Urgency and frequency
    • Symptoms for at least 6 weeks
  • Diagnosis
    • Clinical diagnosis after exclusion of other diagnoses
    • Urinalysis with microscopy: required to exclude other diagnoses
  • Therapy
    • Behavior modification (first-line): avoid triggers, fluid management based on symptoms, bladder training
    • Oral medications (second-line): Amitriptyline is most commonly used and works as an analgesic and antidepressant.
    • Invasive procedures in the bladder (third-line)

Other differential diagnoses


The differential diagnoses listed here are not exhaustive.


Antibiotic therapy of uncomplicated UTIs

Principles of therapy

First-line treatment for acute uncomplicated cystitis in nonpregnant women

Second-line treatment

Antibiotic therapy of complicated UTIs

Therapy in pregnant women

Treatment of recurrent infections

  • Chemoprophylaxis can be given to patients with > 2 UTIs per year.
    • Postcoital prophylaxis or at the onset of initial symptoms with a single dose of TMP-SMX
    • Continuous prophylaxis with low-dose TMP-SMX for 6 months.



We list the most important complications. The selection is not exhaustive.


  • Increased fluid intake
  • Postcoital voiding
  • Intermittent straight catheterization is preferred in patients with neurogenic bladder.
  • Intermittent catheterization, instead of the placement of an indwelling catheter, also reduces catheter-associated UTIs
  • Prophylaxis in recurrent urinary tract infections (see “Treatment of recurrent infections” above)


Special patient groups

UTI during pregnancy

UTI in children and adolescents

  • Diagnosis
    • Urinalysis and urine culture
      • Criteria for diagnosis includes both a positive urinalysis; (pyuria; and/or bacteriuria; ) and urine culture (> 50,000 CFU/mL).
      • A clean-catch urine sample may be obtained if the child is toilet trained. If not trained, a straight catheterization is necessary.
      • Indicated in patients with suspected UTI that fulfill one of the following criteria:
        • Females and uncircumcised males of < 24 months of age with one of the following risk factors: either fever of unknown source or of duration > 24 hours, history of UTI, ill appearance, suprapubic tenderness, or nonblack race
        • Circumcised boys < 24 months of age with at least two of the above risk factors
        • Children older than 24 months with a suspected UTI based on urinary symptoms (see “Clinical features” section)
        • Any febrile infant or child with an abnormal urinary tract or family history of urinary tract disease
    • Renal and bladder ultrasound
      • Indications:
        • Infants aged 2–24 months with a febrile UTI
        • Children with either treatment failure, abnormal voiding, abdominal mass, recurrent UTI, or poor likelihood of follow-up
    • Voiding cystourethrography (VCUG) indicated in abnormal ultrasound (hydronephrosis, obstruction, scarring, or masses), abnormal voiding pattern, or recurrent UTI
  • Treatment