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Urinary tract infections

Last updated: September 15, 2021

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Urinary tract infections (UTIs) are infections of the bladder, urethra, ureters, or kidneys that are most commonly caused by bacteria, especially E. coli. Infections of the bladder or urethra are called lower UTIs, whereas infections involving the kidneys or ureters are called upper UTIs. Because women have a shorter urethra and anal and genital regions that are closer in proximity, they are at higher risk of contracting UTIs than men. Other risk factors include sexual intercourse, indwelling urinary catheters, pregnancy, and abnormalities of the urinary tract. UTIs in otherwise healthy, nonpregnant, and premenopausal women are considered uncomplicated. UTIs in men or patients with other risk factors for treatment failure or serious outcomes, such as functional or anatomical abnormalities of the urinary tract, are considered complicated. 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 cause fever and flank pain. Diagnosis is usually clinical and can be supported with findings of pyuria and bacteriuria on urinalysis. Further evaluation with urine culture and/or imaging may be required for patients with complicated cystitis or equivocal urinalysis findings. Antibiotic treatment regimens depend on the location and severity of infection. First-line empiric antibiotic therapy options for uncomplicated lower UTIs include oral nitrofurantoin, trimethoprim-sulfamethoxazole, and fosfomycin for up to 7 days. For complicated lower UTIs, broad-spectrum antibiotic therapy should be given for 7–14 days and treatable complicating factors should be addressed. Recurrent UTIs are common in women and antibiotic prophylaxis may be indicated. Catheter-associated urinary tract infections (CAUTI) are among the most common healthcare-associated infections; they are frequently caused by resistant bacteria and are treated with catheter removal or replacement in addition to antibiotic therapy. Pregnant women should be screened and treated both for UTIs and for asymptomatic bacteriuria. For the management of upper UTIs, see “Pyelonephritis.”




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.

Urinary tract infections are classified and treated based on location, severity, source of infection, and frequency. The presence of symptoms distinguishes UTI from asymptomatic bacteriuria, which only requires treatment in a select subset of patients.

Classification of urinary tract infections [7]
By clinical presentation [8] Asymptomatic bacteriuria (ASB)
Urinary tract infection (UTI)
By location [9] Lower UTI

Upper UTI

By severity [10][11][12] Uncomplicated UTI
  • Infection in nonpregnant, premenopausal women without further risk factors for infection, treatment failure, or serious outcomes
Complicated UTI (cUTI)
  • UTI that leads to life-threatening organ dysfunction (see “Sepsis”) [13]
By source of infection [14][15] Community-acquired UTI
  • UTI acquired outside of a healthcare setting and/or UTI that manifests within 48 hours of hospital admission
Healthcare-associated UTI
By frequency [8] Recurrent UTI
  • ≥ 3 episodes of symptomatic, culture-proven UTI in one year or ≥ 2 episodes in 6 months

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

Approach [7][22]

Symptomatic, uncomplicated lower UTIs can be diagnosed clinically. In all other patients, urinalysis is the most important initial diagnostic test.

UTI is primarily a clinical diagnosis that is supported by typical findings on urinalysis. Urine culture is indicated in select cases to determine the causative pathogen and adapt antibiotic treatment.

Laboratory studies [23]

Urinalysis [23][24]

Urine culture [7][12][23]

In patients with complicated or recurrent urinary tract infections, a urine culture should be obtained prior to initiating antibiotic treatment. False negative results are possible if a culture is obtained after the patient has received antibiotics.

Additional diagnostics [13][22][30]

Imaging [12][13][31]

Imaging is generally not indicated or helpful for the diagnosis of lower UTI, but it may be performed in select patients to rule out complicating factors (e.g., urinary tract obstruction) or if complicated pyelonephritis or urosepsis are suspected. For imaging indications and findings in upper UTI, see “Diagnostics” in “Pyelonephritis.”

Imaging is not routinely necessary for patients with uncomplicated lower UTI.

Interstitial cystitis (painful bladder syndrome) [32][33]

Asymptomatic bacteriuria (ASB) [25][39]

  • 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 CFU/mL in one sample in women or men
  • Management

Other differential diagnoses

The differential diagnoses listed here are not exhaustive.

General principles [7][12][22][42]

  • Antibiotic treatment is recommended for all patients with symptomatic UTI.
    • The optimal therapy depends on disease severity, local resistance patterns, and patient characteristics (e.g., allergies).
    • Initial treatment is with an empiric regimen, which is maintained for uncomplicated cystitis.
    • In unclear or complicated cases, the regimen may subsequently have to be adjusted based on urine culture data.
  • Consider the need for supportive treatment.
    • Phenazopyridine, a urinary analgesic, can be used for symptomatic relief for a maximum of 2 days.
    • Oral analgesia, e.g., with NSAIDs, can provide additional relief.
  • For the treatment of upper UTI, see “Treatment of pyelonephritis.”

Uncomplicated lower UTI [12][42][43]

  • Management can typically be done in the outpatient setting with oral therapy.
  • Treatment duration depends on the chosen antibiotic agent.
  • Symptom relief can be expected to occur after an average of 36 hours. [28]
  • Persistent symptoms despite antibiotic therapy suggest complicated UTI and/or indicate the need to change the empiric therapy.

Antibiotic treatment of uncomplicated lower UTIs

Complicated lower UTI [7][12][44][45]

Antibiotic treatment of complicated lower UTIs [12][44]

Treatment regimens for UTI in men should include antibiotics that are able to penetrate prostate tissue (e.g., fluoroquinolones or TMP-SMX). Fosfomycin or nitrofurantoin are generally not adequate.

Management of complicating factors

  • Nephrolithiasis: In UTI with renal obstruction, urgent urology consultation is required for drainage. [48]
  • Indwelling medical devices (e.g., ureteral stents, percutaneous nephrostomy tubes) [49][50]
    • Management of infections may require exchange or removal of the device, especially when it is obstructed.
    • Urology should be consulted urgently for further management.
  • Other treatable factors should be addressed: e.g., optimal blood sugar control for diabetics.

Recurrent UTI [8][51]

Recurrent UTIs are common in women. Management involves the implementation of preventive measures and antibacterial prophylaxis in addition to the antibiotic treatment of acute episodes.

Acute management

Chemoprophylaxis [8]

Nonantibiotic prophylaxis

  • Cranberry products have shown moderate benefit and are associated with little risk.
  • Topical estrogen therapy should be considered in postmenopausal women.
  • Behavioral modifications (e.g., increased fluid intake, postcoital voiding) may be helpful.

Candiduria [52]

  • Candida isolated from the urine rarely indicates systemic infection, but it may be a marker for greater mortality in severely ill patients.
  • Predisposing factors should be treated in all cases of candiduria, e.g., by removing indwelling catheters whenever possible.
  • Indications for antifungal treatment include symptomatic cystitis or pyelonephritis, neutropenia, or a planned urologic procedure.
  • Commonly used antifungals include fluconazole and amphotericin B.
  • Consult the infectious disease service for assistance with appropriate antifungal treatment.

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

Overview [12][14]


A urine culture, ideally obtained prior to antibiotic treatment, is always required to diagnose CAUTI.

  • Indications: features consistent with potential infection
  • Specimen collection: ideally from the sampling port of a newly inserted device using aseptic technique [56]
  • Diagnostic criteria


UTI in elderly patients [57]

  • UTI is very common in advanced age, both in individuals who live in long-term care facilities and those who do not.
  • Symptoms of UTI are more commonly atypical (e.g., back pain, pelvic pain, constipation, urinary incontinence, and altered mental status).
  • Management principles are generally the same as outlined above.
  • Preventative strategies include increasing mobility and consumption of cranberry products.

UTI during pregnancy [58]


Asymptomatic bacteriuria in pregnancy [12][59]

Treatment of ASB and lower UTIs in pregnant women [12][60]

Although UTI in pregnant patients is generally considered complicated, treatment regimens may include those typically used for uncomplicated UTI and should be adapted to the patient's individual risk and urine culture results.

Asymptomatic bacteriuria in pregnancy is a risk factor for pyelonephritis and should be treated.

UTI in children and adolescents [61][62]


  • 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



  • 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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