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Urinary tract infections

Last updated: May 28, 2021

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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

  • Sexual intercourse
    • Honeymoon cystitis; : a type of lower UTI that occurs in women after having sexual intercourse for the first time or after a prolonged period of abstinence.
    • Diaphragm and spermicide use
  • Catheter-associated urinary tract infection (CAUTI)

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]

  • Uncomplicated UTI: UTI in immunocompetent, premenopausal, nonpregnant women without conditions predisposing them to infection or therapy failure
  • Complicated UTI: UTIs in men, pregnant or postmenopausal women, children, and individuals with factors predisposing them to infection or therapy failure. Such factors include:

According to source of infection

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]


Urine culture

Diagnostic imaging

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; more often 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]

  • Supportive treatment (increased fluid intake) may be sufficient, but antibiotic therapy should be recommended.
  • Empiric treatment can be given for uncomplicated cystitis.
  • Local resistance patterns should guide the choice of empiric therapy.
  • Persistent symptoms after 48–72 hours of antibiotic therapy suggest possible complicated cystitis and/or indicate the need to change the empiric therapy.
  • Phenazopyridine, a urinary analgesic, can be used for dysuria for 1–3 days.
  • Urine cultures after treatment are not required if the patient's symptoms resolve. [31]

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
    • Continuous prophylaxis with low-dose TMP-SMX for up to 6 months

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

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
  • 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.
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