Urinary Tract Infection (UTI)

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A urinary tract infection (UTI) is an inflammatory reaction of the urinary tract epithelium (affecting the kidneys, bladder, or urethra) in response to pathogenic microorganisms,Β most commonly bacteria.

As one of the most common infections, UTIs affect 150 million people each year worldwide, with peak incidence among young, sexually active women aged 18 to 24.1

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Cystitis, also referred to as a lower UTI, is a bladder infection. This is also categorised as an uncomplicated UTI, though it can progress to an upper or complicated UTI.

Pyelonephritis, also referred to as upper or complicated UTI, is an infection of the kidney that often occurs via bacterial ascent.

Recurrent bacterial cystitis is defined as two or more UTIs in six months or three or more in 12 months.


Urinary tract infections (UTIs) are caused by a wide range of pathogens, including Gram-negative and Gram-positive bacteria, as well as fungi.

The causative organism may vary depending on whether the UTI is community-acquired or healthcare-acquired, and prior exposure of the patient to antimicrobials.2

The most common causative agent is uropathogenic Escherichia coli, followed by Klebsiella pneumoniae, and Enterococcus faecalis.3

Risk factors

Risk factors vary slightly depending on sex, which is an independent risk factor.

Females are 30 times more likely than males to develop a UTI due to the shorter urethra. As a result, there is a greater probability of bacteria reaching the bladder before being expelled in urine, as the space between the opening of the urethra and the bladder is shorter.4

For females, risk factors to consider include:5

  • Sexual activity
  • Pregnancy
  • Incontinence
  • Post-menopause: absence of oestrogen (consistent with vaginal atrophy, also known as genitourinary syndrome of menopause)
  • Presence of a cystocele
  • Positive family history of UTIs

For males, risk factors to consider include:6

  • Benign prostatic hypertrophy
  • Urethral strictures

In both sexes, the following are risk factors:3,5,6

  • Previous history of UTI
  • Presence of a foreign body: any indwelling catheter or foreign body (e.g. stone, suture, surgical material, or exposed polypropylene mesh from pelvic surgery) significantly increases the risk for UTI
  • Diabetes mellitus

In children, risk factors to consider are uncircumcision and vesicoureteral reflux (VUR), which is found in approximately 25% of children with first-time UTI.7

Clinical features


Typical symptoms of lower and uncomplicated UTIs (cystitis) include:8

  • Dysuria: feeling of pain, discomfort or burning sensation while urinating
  • Urgency: an unstoppable urge to urinate due to sudden involuntary contraction of the bladder muscles
  • Frequency: urinating too often and at frequent intervals
  • Hesitancy: inability to start the urine stream
  • Suprapubic pain
  • New-onset nocturia: waking during the night to urinate
  • New-onset urinary incontinence: loss of bladder control
  • Haematuria: blood in the urine

Irritability, poor feeding, and fever (>39Β°C) are non-specific symptoms commonly seen in neonates and infants

Symptoms more indicative of upper and complicated UTIs (pyelonephritis) include:

  • Flank pain
  • Fever and chills
  • Nausea and vomiting

Typical symptoms of recurrent UTIs (cystitis) include:

  • Recurrent dysuria, urgency and frequency
  • Suprapubic pain
  • Cloudy urine
  • Pelvic pain

Other important areas to cover in the history include:

  • Hydration and diet history
  • Prior history of UTIs
  • Sexual history (e.g. assess for risk of sexually transmitted infections)
  • Medication history (e.g. recent antibiotic history, immunosuppressive drugs)

For more information, see the Geeky Medics guide to urological history taking.

Clinical examination

In the context of a suspected UTI, a thorough abdominal examination is required.

Typical clinical findings in UTI include:

  • Suprapubic tenderness
  • Costovertebral tenderness, if kidney involvement (pyelonephritis)

Differential diagnoses

Differential diagnoses to consider in the context of a suspected UTI include:1


Bedside investigations

Relevant bedside investigations include:

  • Basic observations (vital signs): to assess for systemic features (e.g. fever/tachycardia) which may suggest pyelonephritis
  • Urinalysis: to assess for the presence of nitrites, leukocyte esterases, protein, and haematuria.
  • Urine pregnancy test (hCG urine dipstick): to rule pregnancy in or out. This investigation is relevant, as UTIs are common in pregnant women, and pregnancy will influence management, including antibiotic options.

Laboratory investigations

Relevant laboratory investigationsΒ include:

  • Urine microscopy, culture and sensitivity (MC&S): enables visualisation and quantification of white blood cells, red blood cells, and bacteria or yeast if present. If bacteria are present, culture and sensitivity testing allows for guidance on antibiotic sensitivity.Β 

Always send MC&S in cases of complicated or recurrent UTI.Β 


The diagnosis of a UTI is made from the clinical history (symptoms) and urinalysis and can be further confirmed by a urine culture (with quantification and sensitivity testing), if necessary.

The following findings would be diagnostic on urinalysis:

  • Nitrites: strongly suggestive of bacteriuria, as nitrates are broken down into nitrites only in the presence of bacteria.
  • Leukocyte esterases: an enzyme leukocytes produce in response to bacteria in the urine.

OnΒ MC&S, the following findings would be consistent with a UTI:

  • Bacteriuria: the presence of bacteria in urine. Historically, β‰₯ 105 bacterial colonies/mL of urine were needed to diagnose a UTI. However, a UTI can be diagnosed if the symptoms are present with as low as 102 bacterial colonies/mL. If there is bacteriuria without symptoms, this is termed asymptomatic bacteriuria. It is more common in older patients, and asymptomatic bacteriuria is only treated in pregnant women, before urological operations or if there are associated symptoms.
  • Pyuria: the presence of WBCs in the urine. Sterile pyuria (WBCs in the urine, without infection) can indicate a range of diagnoses, including renal malignancy, pelvic malignancy and genitourinary tuberculosis.


Conservative management

Most UTIs will spontaneously resolve in about 20% of females, especially with increased hydration.

Lifestyle changes which may be beneficial in patients with recurrent UTIs include optimising personal hygiene (wiping front to back for females), using vitamin C as a urinary acidifier, and consumption of D-mannose and cranberry products.

Medical management

Lower UTI (cystitis)

Simple analgesia (paracetamol and ibuprofen) can be used for pain relief.Β 

Three- or seven-day regimens of nitrofurantoin and trimethoprim are the recommended oral antibiotics as first-line therapy for lower/uncomplicated UTI in men, non-pregnant women, and children.

NICE guidelines recommend checking any previous urine cultures, susceptibility results and antibiotic prescribing before choosing an antibiotic.

In pregnant women, trimethoprim is contraindicated.

In individuals with an eGFR β‰₯ 45 ml/minute, nitrofurantoin is preferred, as it is renally excreted.9

Upper UTI (pyelonephritis)

Simple analgesia (paracetamol and ibuprofen) with or without a weak opioid (e.g. codeine) can be used for pain relief.Β 

Cefalexin and co-amoxiclav are the recommended oral antibiotics as first-line therapy for upper UTIs/acute pyelonephritis in men, non-pregnant women, and children.

NICE guidelines recommend checking any previous urine cultures, susceptibility results and antibiotic prescribing before choosing an antibiotic.

If oral antibiotics are not tolerated or the patient is severely unwell, intravenous antibiotics should be used.

In pregnant women, cefalexin is the first-line oral antibiotic, and cefuroxime is the first-line IV antibiotic.10

UTIs in children

Babies under three months with a suspected UTI should be urgently referred to paediatrics for intravenous antibiotics.

Children and babies may require imaging to assess for structural abnormalities (e.g. vesicoureteric reflux) and/or renal scarring. Imaging options include ultrasound, micturating cystourethrography (MCUG) and dimercaptosuccinic acid (DMSA) scanning.

The imaging modality depends on the child’s age and the clinical presentation. Further details can be found in the NICE guidelines.Β 

Recurrent UTI

Prophylactic oral antibiotics (cephalexin, nitrofurantoin and trimethoprim) are first-line recommendations in individuals with recurrent UTIs.

These are to be taken daily or postcoitally, usually for 6 to 12 months, though this can be extended. A urinary antiseptic can be added, such as methenamine hippurate.

In post-menopausal patients, vaginal oestrogen should also be considered.11,12


If urinary tract infections continue untreated, complications which may occur include:3

  • Persistent lower urinary tract symptoms
  • Staghorn urinary calculi
  • Pyelonephritis
  • Emphysematous pyelonephritis and cystitis
  • Incontinence
  • Renal abscess
  • Prostatic abscess
  • Chronic prostatitis
  • Hypertension
  • Renal failure

Key points

  • A urinary tract infection is the inflammation of the urinary tract epithelium, most commonly in response to bacterial infection.
  • UTIs can occur in any part of the urinary tract, including the kidneys, ureters, bladder, and urethra.
  • Risk factors include female sex, pregnancy, urethral strictures, obstructions, uncircumcision, and foreign bodies.
  • Urinalysis is the main bedside investigation for suspected UTIs.
  • The diagnosis of UTI involves the clinical history, urinalysis, and urine microscopy, culture and sensitivity (MC&S).
  • Management includes lifestyle modifications such as increased fluid intake, personal hygiene, and antibiotics (e.g. trimethoprim and nitrofurantoin).
  • Common complications of UTIs include persistent or recurrent infections, pyelonephritis, incontinence, and renal stones.


Mr Derek Hennessy

Consultant Urologist

Mercy University Hospital, Cork, Ireland


Dr Chris Jefferies


  1. Stamm WE, Norrby SR. Urinary tract infections: disease panorama and challenges. Published in 2001. Available from: [LINK].
  2. Li R, Leslie SW. Cystitis. StatPearls. Published 2022. Available from: [LINK].
  3. Bono MJ, Leslie SW, Reygaert WC. Urinary Tract Infection. StatPearls. Published in 2022. Available from: [LINK].
  4. Foxman B. Epidemiology of urinary tract infections: incidence, morbidity, and economic costs. Published in 2002. Available from: [LINK].
  5. BMJ Best Practice. Urinary tract infections in women. Published in 2021. Available from: [LINK].
  6. BMJ Best Practice. Urinary tract infections in men. Published in 2021. Available from: [LINK].
  7. BMJ Best Practice. Urinary tract infections in children. Published in 2021. Available from: [LINK].
  8. Kaur R, Kaur R. Symptoms, risk factors, diagnosis and treatment of urinary tract infections. Postgrad Med J. Published in 2021. Available from: [LINK].
  9. NICE. Urinary tract infection (lower): antimicrobial prescribing. Published in 2018. Available from: [LINK].
  10. NICE. Pyelonephritis (acute): antimicrobial prescribing. Published in 2018. Available from: [LINK].
  11. NICE. Urinary tract infection (recurrent): antimicrobial prescribing. Published in 2018. Available from: [LINK].
  12. Anger J, Lee U, Ackerman AL, et al. Recurrent Uncomplicated Urinary Tract Infections in Women: AUA/CUA/SUFU Guideline. Published in 2019. Available from: [LINK].


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