• Clinical science

Urinary tract infections


Urinary tract infections (UTIs) are infections of the urinary tract system (bladder, urethra, kidneys) that are generally caused by bacteria, especially E. 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. Clinical findings depend on which part of the urinary tract is affected. Lower UTIs manifest with dysuria, suprapubic pain, urinary urgency, and increased urinary frequency, whereas upper UTIs additionally manifest with fever and flank pain. Diagnosis is usually clinical and can be supported with findings of pyuria, bacteriuria, and positive leukocyte esterase and nitrites on urinalysis. Further evaluation with urine culture and/or imaging may be required for patients with complicated cystitis. Treatment likewise depends on which part of the urinary tract is affected. First-line empiric antibiotic therapy for uncomplicated UTIs includes outpatient therapy with oral trimethoprim-sulfamethoxazole, nitrofurantoin, or fosfomycin for up to 7 days. For complicated UTIs antibiotic therapy should be extended for 7–14 days. Pregnant women with cystitis should be screened and treated if positive for asymptomatic bacteriuria.





Other pathogens

Predisposing factors

Host-dependent factors

Other factors

SEEK PP = S - S. saprophyticus, E - E. coli, E - Enterococcus, K - Klebsiella, P - Proteus, P - Pseudomonas are the bacteria commonly associated with UTIs.


According to anatomic location [7][8]

According to predisposing factors [9][10][11]

According to source of infection

  • Community-acquired: UTI acquired outside of the hospital setting that manifests within 48 hours of hospital admission. [12]
  • Healthcare-associated (nosocomial) UTI
  • Recurrent UTI: ≥ 3 infections in one year or ≥ 2 infections in 6 months

Clinical features

Since fever is usually absent in lower UTIs, the presence of fever and flank pain should be taken as a sign of more serious infection, e.g., pyelonephritis.



Laboratory tests [14][17]


  • Overview
    • Best initial test
    • Individuals with predisposing factors have an increased risk of infection or therapy failure (see “Complicated UTI” in “Classification”).
  • Urinalysis collection method
    • Clean-catch midstream sample: necessary to avoid contamination with vaginal or skin flora
    • Straight catheterization of the bladder or suprapubic aspiration: performed if a clean catch cannot be obtained without contamination (e.g., in children who are not toilet trained)
    • Urethral catheterization is contraindicated due to increased risk of bacteremia.
  • Diagnostic criteria for UTI
    • Pyuria: ≥ 5–10 WBC/HPF
    • Bacteriuria: abnormal number of bacteria present in urine sample (≥ 106 organisms/mL)
  • Findings indicative of UTI [18]
  • Other findings

Urine culture

Diagnostic imaging

Differential diagnoses

Interstitial cystitis (painful bladder syndrome) [19][20]

Asymptomatic bacteriuria [26][27]

  • Description
    • Presence of ≥ 100,000 CFU/mL in at least two voided urine samples in patients with no symptoms of UTI; (e.g., dysuria, frequency, urgency, suprapubic pain)
    • Bacteriuria typically resolves spontaneously in healthy, nonpregnant women without any side effects.
    • Women with asymptomatic bacteriuria may progress to symptomatic UTI in the future; than women with no bacteriuria.
  • Epidemiology
    • Prevalence
      • Occurs in 1–5% of healthy, premenopausal women and in 2–10% of pregnant women
      • Occurs in 9–25% of elderly individuals and individuals with diabetes, indwelling catheters, or spinal cord injuries
  • Etiology: E. coli is the most common causative organism.
  • Risk factors
  • Diagnosis: urinalysis with microscopy
    • Mid-stream urine sample: bacterial growth ≥ 100,000 CFU/mL in two consecutive samples in women or in one sample in men
    • Catheterized urine sample: bacterial growth ≥ 100,000 CFU/mL with one bacterial species isolated in women or men
  • Management
    • Treatment is recommended in:
    • Treatment is not recommended in:
      • Healthy, nonpregnant women
      • Elderly individuals and individuals with diabetes, indwelling catheters, or spinal cord injuries

Other differential diagnoses

The differential diagnoses listed here are not exhaustive.


Antibiotic therapy for uncomplicated UTIs

Principles of therapy [14][30]

Treatment of acute uncomplicated lower UTIs

Treatment of uncomplicated upper UTIs

See “Treatment” section for “Pyelonephritis.”

Antibiotic therapy for complicated UTIs

Treatment is generally given for 7–14 days in complicated UTIs.

Antibiotic therapy for recurrent infections [26][27]

  • If the patient becomes symptomatic within 2 weeks after treatment of a UTI, the patient can be restarted on the same treatment for 2 additional weeks and a urine culture should be obtained.
  • A single recurrent infection can be treated in the same way as an uncomplicated UTI.
  • Chemoprophylaxis can be given to patients with recurrent UTIs.
    • Postcoital prophylaxis
      • Nitrofurantoin or a single dose of TMP-SMX
      • Postcoital prophylaxis should be considered in women with a history of recurrent UTIs who wish to conceive.
    • Continuous prophylaxis with low-dose TMP-SMX for up to 6 months


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


  • Behavioral modifications [37]
    • Increased fluid intake
    • Timely bladder voiding
    • Postcoital voiding
    • Adequate genital hygiene
  • Intermittent straight catheterization
  • Prophylaxis: indicated for recurrent urinary tract infections (see “Treatment of recurrent infections” above)

Special patient groups

UTI during pregnancy

UTI in children and adolescents [40][41]

  • Epidemiology
    • UTIs are common in children.
    • Approx. 8% of girls and 2% of boys will have had a UTI by the age of 7 years.
  • Risk factors
  • Diagnosis
    • Urinalysis and urine culture are indicated in patients with suspected UTI that fulfill one of the following criteria
      • Any febrile infant or child with an abnormal urinary tract or family history of urinary tract disease
      • Circumcised boys < 12 months of age with: fever or no obvious cause of infection
      • Female and uncircumcised male children between 2–24 months of age with one of the following: history of previous UTI, fever of unknown source or duration > 24 hours, ill appearance, suprapubic tenderness
      • Children > 24 months with a suspected UTI based on urinary symptoms (see “Clinical features” above)
    • Criteria for diagnosis includes both a positive urinalysis (pyuria and/or bacteriuria) and urine culture (> 50,000 CFU/mL).
    • Renal and bladder ultrasound indicated in:
      • Children 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) used in:
  • Treatment
    • Treatment principles in children are similar to those in adults.
    • Empiric therapy
    • When associated with structural abnormalities, additional management of the underlying condition may be required.