Overview

A lower urinary tract infection (UTI) describes an infection of the bladder with no evidence of urethritis, prostatitis, epididymitis, or orchitis, usually by bacteria, but rarely by other pathogens including fungi, viruses, and parasites.

Cystitis is often used interchangeably with lower UTI, however, this means inflammation of the bladder which may also be due to non-infectious causes, although they are rare.

Causes

Overview

UTI is usually caused by gastrointestinal tract bacteria entering the urinary tract by ascending through the urethra into the bladder, via the blood (more likely if immunosuppressed), or directly (e.g. inserting catheters).

Escherichia coli is the most common causative organism and makes up 80% of cases.

Less common causes include:

  • Staphylococcus saprophyticus – 4%
  • Klebsiella pneumoniae – 4%
  • Proteus mirabilis – 4%
  • Candida albicans – rare, but associated with people who are immunosuppressed or have indwelling catheters

Epidemiology

  • UTI is much less common in men than women as women have shorter urethras
  • Acute UTI occurs in up to 50% of women, around 1/3 of women have UTI by 24 years old
  • UTIs are more common in older women
  • UTI is rarely seen in men <50 years old

Definitions

An upper UTI describes infection of the upper urinary tract including pyelitis (infection of the proximal ureters) and pyelonephritis (infection of both the kidneys and proximal ureters).

An uncomplicated UTI describes a UTI caused by a typical pathogen in a person with a normal urinary tract and normal kidney function.

A complicated UTI describes a UTI with an increased risk of complications including persistent infection, recurrent infection, or treatment failure.

Recurrent UTI describes repeated UTIs due to relapse or re-infection and is defined as:

  • ≥3 UTIs in the last 12 months or
  • ≥2 UTIs in the last 6 months

A relapse is a recurrent UTI with the same strain of microorganism and is usually seen within a short time after treatment (around 2 weeks).

A re-infection is a recurrent UTI with a different strain or species of micro-organism and is usually seen more than 2 weeks after treatment.

Asymptomatic bacteriuria describes the presence of bacteria in the urine without signs or symptoms of infection. This is due to bacterial colonisation of the urinary tract.

Catheter-associated UTI describes a symptomatic infection of the urinary tract in a person who is catheterised or has been catheterised in the last 48 hours.

  • The longer a catheter has been inserted, the more likely bacteria will be found in the urine. This may be asymptomatic and may not require treatment.

Risk Factors

Risk factors for UTI include:

  • All people:
    • Sexual intercourse
    • Previous UTI
    • Diabetes mellitus
    • Antibiotic use – changes flora in the genital region and may promote infection
    • Urinary tract abnormalities (e.g. vesicoureteral reflux)
    • Immunosuppression
    • Recent hospitalisation
    • Urinary incontinence
    • Catheterisation or other urinary tract instrumentation/surgery
  • For men:
  • For women:
    • Atrophic vaginitis
    • Cystocele
    • Institutionalisation

Presentation

Overview

Features suggesting a UTI include:

  • Dysuria – pain when passing urine, often describes as burning or stinging
  • Frequency – passing urine more often than usual
  • Urgency – a strong desire to pass urine immediately, may lead to incontinence
  • Nocturia – passing urine at night more often than usual
  • Suprapubic tenderness – suggests cystitis
  • Changes in urine:
  • Low-grade fever – a higher fever may suggest pyelonephritis

In older people, especially if they have cognitive impairment, typical features may not be present. UTI may present as:

  • Acute worsening of dementia/development of delirium – the reasons for this are unknown:
  • Non-specific features – lethargy, anorexia, reduced ability to carry out activities of daily living

Other causes of infection/delirium must be ruled out before a diagnosis of UTI is made.

Investigations

Overview

No combination of symptoms and dipstick tests are completely reliable in diagnosing UTI, therefore, criteria are in place to guide investigating UTI. All people should also be given safety-netting advice if symptoms worsen.

In women

  • If <65 years old and not catheterised: perform a urine dipstick:
    • Positive for nitrites or leukocytes + red blood cells: UTI likely
    • Negative for nitrites but positive for leukocytes: UTI equally likely to other diagnoses
    • Negative for all nitrites, leukocytes, and red blood cells: UTI unlikely, consider alternate diagnosis
  • Arrange a urine culture if any of the following apply:
    • >65 years old – dipsticks are unreliable in people >65 years old
    • Catheterised – dipsticks are unreliable
    • Pregnant – even if UTI seems less likely to reduce the risk of complications (e.g. pyelonephritis)
    • Visible or non-visible haematuria – to confirm that haematuria is likely due to UTI and less likely to be due to another cause (e.g. malignancy) 
    • Recurrent UTI
    • Persistent symptoms/unresponsive to antibiotics
    • Atypical symptoms
    • Risk factors for complicated UTI (e.g. renal impairment, anatomical abnormalities, prolonged hospitalisation, long-term care facility residence)

In men

  • Send a urine culture
  • Urine cultures and dipsticks must not be used to diagnose UTI in men if any of the following apply:
    • >65 years old – dipsticks are less reliable with increasing age
    • Catheterisation – dipsticks are unreliable in catheterised people
  • Similarly to women, other indications for urine culture include haematuria, recurrent UTI, persistent symptoms/unresponsive to antibiotics, atypical symptoms, or risk factors for complicated UTI 

Differential Diagnoses

Pyelonephritis

  • There may be a history of UTI present as the infection travels upwards to involve the ureters and kidneys
  • Features of systemic upset suggest pyelonephritis is present, especially fever/rigours, loin pain, and nausea/vomiting

Renal stones

  • Severe, colicky loin pain that radiates to the groin
  • Many patients are restless due to severe pain
  • May co-exist with infection

Acute prostatitis

  • Both may have features of dysuria, frequency, urgency etc. but prostatitis has associated pain in the perineum, rectum, or back and obstructed urine flow
  • A digital rectal examination may reveal a tender and boggy prostate
  • Fever is usually higher in acute prostatitis and rigours may be present

Benign prostatic hyperplasia

  • Features of lower urinary tract symptoms (LUTS) may be seen in the absence of dysuria, suprapubic tenderness, or fever is seen
  • Both may have urgency, incontinence, and nocturia

Bladder cancer

  • Most patients present with painless macroscopic haematuria or painless microscopic haematuria found incidentally
  • There may be a history of exposure to chemical agents such as aniline dyes and rubber, or Schistosomiasis

Renal cancer

  • Patients may have a classic triad of haematuria, loin pain, and an abdominal mass
  • Constitutional symptoms may be seen: fever of unknown origin, unexplained weight loss, anorexia, night sweats
  • Men may have a varicocele that is irreducible or does not diminish when lying down, right-sided varicoceles can suggest a tumour as left-sided ones are more common

Prostate cancer

  • Lower urinary tract symptoms (LUTS) may be seen in addition to haematuria
  • There may be pain in the back, perineum, or scrotal areas
  • A digital rectal examination may identify an irregularly enlarged prostate that is hard and nodular with the loss of the median sulcus 

Sexually transmitted infections (STIs)

  • New or multiple partners may imply an increased risk, particularly if barrier methods of contraception (e.g. condoms) have not been used
  • Gonorrhoea tends to be symptomatic more often than Chlamydia
  • Features suggesting an STI include dysuria, urethral discharge (especially if purulent), changes in vaginal discharge colour, consistency, or amount
  • People may be given treatment for a UTI but still have persisting symptoms

Overactive bladder

  • Urinary frequency and urgency are present, but no dysuria, fever, or suprapubic tenderness is present

Interstitial cystitis

  • Difficult to distinguish from UTI clinically
  • Flares and remissions of suprapubic pain, dysuria, and pelvic pain with negative urinalysis results

Asymptomatic bacteriuria

  • No symptoms of UTI are present, but dipstick testing shows the presence of nitrites
  • This is common and may affect up to 1/5 of women, prevalence is even higher in those who are in care homes or catheterised

Management

Overview

Follow local antibiotic guidelines if available. The BNF has national guidelines regarding antibiotic choices which are tested in exams.

Non-pregnant women

In non-pregnant women:

  • 1st-line: trimethoprim or nitrofurantoin for 3 days
  • If not already done, send a urine culture if:
    • >65 years old – dipsticks are unreliable
    • Visible/non-visible haematuria – to ensure haematuria is more likely to be due to UTI

Pregnant people

In pregnant people:

  • All pregnant people should have urine cultures sent
  • If symptomatic, options depend on how many weeks gestation:
    • 1st-line: nitrofurantoin but avoid near term as this can cause neonatal haemolytic anaemia and prolonged neonatal jaundice
    • 2nd-line: amoxicillin or cefalexin
    • Trimethoprim is teratogenic, especially in the first trimester (as it inhibits folate metabolism), therefore it should be avoided in pregnancy
  • If asymptomatic bacteriuria:
    • 1st-line: treat as above, even if asymptomatic
      • This is to reduce the risk of complications such as pyelonephritis
    • Urine cultures are routinely performed at the first antenatal visit
    • After treatment, a further urine culture should be arranged as a test of cure

Men

In men:

  • 1st-line: trimethoprim or nitrofurantoin for 7 days
  • If not already done, send a urine culture in all cases of UTI in men
  • Referral to urology is not routinely done if men have 1 uncomplicated lower UTI, however, refer to urology if any of the following apply:
    • Ongoing symptoms despite antibiotic treatment
    • Underlying risk factors (e.g. bladder outlet obstruction, renal stones, or previous genitourinary surgery)
    • Recurrent UTI

Catheterised non-pregnant patients

In catheterised non-pregnant patients:

  • Do not treat asymptomatic bacteriuria
  • If symptomatic:
    • Give antibiotics (nitrofurantoin or trimethoprim) for 7 days
    • Consider removing or changing the catheter if it has been in place for >7 days

Referral

Acute pyelonephritis

If acute pyelonephritis is suspected, hospital admission may be required. See Acute Pyelonephritis.

Haematuria

If haematuria persists despite UTI treatment, then a referral to secondary care via a suspected cancer pathway may be necessary if it cannot be explained by UTI or another cause.

Monitoring and Patient Advice

Monitoring

Patients are followed up depending on clinical judgement (often after 48 hours) to check the response to treatment and urine culture results.

Patient advice

Patients should be given safety-netting advice and should seek help if symptoms fail to improve, worsen, or if new features arise, such as worsening fever, loin pain, nausea and vomiting, which can suggest acute pyelonephritis.

Patients should be given self-care advice:

  • Drink enough fluid and avoid dehydration
  • Use basic analgesia for pain
  • If appropriate, use protective measures such as condoms during sexual intercourse and avoid delaying passing urine after
  • Wipe from front to back after using the toilet
  • Keep the genital area clean and dry

There is no evidence to support the use of cranberry juice or urine alkalinising agents to treat lower UTIs.

Complications

  • Ascending infection:
    • This can lead to the involvement of the ureters and kidneys and can result in acute pyelonephritis, renal and peri-renal abscesses, renal failure, and sepsis urosepsis
    • Around 3 in 4 people with acute pyelonephritis will have had a preceding UTI
  • Prostatitis:
    • Some men with UTI have bacteria within the prostate which may become involved
  • Pregnancy complications:
    • UTI in pregnancy is associated with preterm delivery and low birth weight
  • Renal stones:
    • More common with Proteus mirabilis infection as its metabolic processes make the urine more alkaline resulting in the formation of struvite stones

Prognosis

  • Acute uncomplicated lower UTI usually resolves within a few days
  • Up to 44% of women with a lower UTI may have recurrence at 12 months

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