The laboratory investigation of urinary tract infections

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The laboratory investigationof urinary tract
infections
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Contents

• Key messages
• Introduction
• Uncomplicated vs complicated UTI
• When is urine culture not helpful?
• When is urine culture helpful?
• Testing for asymptomatic bacteriuria
• Chlamydia trachomatis urethritis

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Key messages

• Women with symptoms of uncomplicated UTI do not
  require a urine culture
• Screening for asymptomatic bacteriuria is not
  recommended except in pregnant women
• Chlamydia trachomatis urethritis can cause
  similar symptoms to a UTI

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Introduction

• Approximately 50 of all women will have a UTI,
  and 25 of these will experience recurrent
  infections
• In 2005, almost 800 000 urine cultures were
  performed in NZ at a cost of approx 12.5
  million
• Patients with asymptomatic bacteria do not
  benefit from antibiotic treatment
• Consider C. trachomatis infection if patients
  present with symptoms of a UTI suspicious
  sexual history

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Uncomplicated versus complicated UTI

• People with symptoms of uncomplicated UTI do not
  require a urine culture. They can be treated
  empirically and no follow-up is required unless
  symptoms do not improve.
• People with complicated UTI require urine testing
  for culture and susceptibility testing

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• Uncomplicated UTI

Classic presentation dysuria, frequency urgency suprapubic pain Occurs in women with a normal, unobstructed genitourinary tract. Most frequent in young sexually active women.
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Complicated UTIs are those occurring in
Men Children Pregnancy People with suspected pyelonephritis People with recurrent UTI Failed antibiotic treatment or persistent symptoms Catheterised patients Hospital-acquired infections Recent urinary tract instrumentation People with abnormalities of genitourinary tract People with renal impairment and People with impaired host defences
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Urine culture is not helpful for women with
uncomplicated lower urinary tract infections as
it does not improve outcomes.

• In women with classical presentation of
  uncomplicated UTI, treatment can begin based on
  the strength of clinical presentation.
• In women with dysuria and vaginal symptoms
  consider both a UTI and STIs.
• A dipstick positive to nitrites or leukocytes has
  a probability of a UTI of about 80
• A dipstick negative to both nitrites and
  leukocytes, has a probability of a UTI of about
  20.

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When is urine culture helpful?

• Urine culture should be performed for
• Women with a UTI with complicating features
• All pregnant women
• Men with suspected UTI
• Suspected acute pyelonephritis
• Prostatitis

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Complicating features in women include

• Abnormal urinary tract e.g. stone, reflux,
  catheter,
• Impaired host defences e.g. pregnancy, diabetes,
  immunosupression,
• Impaired renal function,
• Suspicion of pyelonephritis,
• More than three UTIs in one year, or
• UTI recurrence within two weeks.

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Urine culture is recommended for pregnant women

• Women with asymptomatic bacteriuria in early
  pregnancy have a 20-30 fold increased risk of
  developing pyelonephritis, premature delivery and
  low birth weight infants.
• All pregnant women should be screened for
  asymptomatic bacteriuria at 12-16 weeks
  gestation.
• If bacteriuria is detected by screening, the
  patient should be treated and a urine culture
  performed monthly throughout the pregnancy

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Urine culture is indicated for lower UTI in Men

• All UTIs in men are considered complicated,
  therefore a urine culture is indicated, even if
  the urine dipstick is negative.

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A urine culture is indicated when acute
pyelonephritis is suspected

• Dipstick testing of the urine may be useful if
  clinical findings are equivocal
• Antibiotics should be commenced while waiting for
  culture results
• Post-treatment urine cultures are recommended one
  to two weeks after antibiotic therapy

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Acute Prostatitis

• Signs and symptoms of acute prostatitis include
  fever, dysuria, pelvic or perineal pain, and
  cloudy urine
• Urine culture should be performed
• If urine culture is negative, STIs (C.
  trachomatis, N. gonorrhoea) should be excluded.

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Chronic Prostatitis

• Chronic prostatitis should be considered in men
  with dysuria and frequency, no signs of acute
  prostatitis, and with recurrent UTIs.
• Gram-negative bacilli are most common cause, but
  enterococci and Chlamydia have been associated
  with chronic infection.

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Screening for asymptomatic bacteriuria
Screening for asymptomatic bacteriuria is not recommended in
Non pregnant women Elderly people People with indwelling urinary catheter. People with spinal cord injuries.

• The prevalence of asymptomatic bacteriuria varies
  from 1-5 to 100 in selected population groups.
• Asymptomatic bacteriuria is a microbiological
  diagnosis based on the isolation of a specified
  count of bacteria in the absence of signs of UTI.

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Testing for asymptomatic bacteriuria not required
in elderly people
Asymptomatic bacteriuria in the elderly occurs
frequently. There is no benefit from treating
asymptomatic bacteriuria. The diagnosis of UTI
in this age group should be made based on
clinical signs and symptoms.
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Regular urine culture or dipstick testing is not
indicated for people with in-dwelling catheters

• All in-dwelling catheters eventually become
  colonised with bacteria.

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Asymptomatic bacteriuria and people with spinal
cord injuries
People with spinal cord injuries have a high
prevalence of bacteriuria, as well as high
incidence of symptomatic urinary tract
infection Urine culture should be performed
when UTI is suspected, for example when the
patient has non-specific symptoms, such as
vomiting and increased spasticity.
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Chlamydia trachomatis urethritis

• Always consider C. trachomatis urethritis when
  UTI is suspected
• C. trachomatis urethritis is commonly
  asymptomatic, but may present with dysuria
• C. trachomatis infection should be considered
  when a UTI is suspected and the patients has a
  suspicious sexual history
• Sterile pyuria (white cells in the urine but no
  urinary pathogen isolated) or positive leucocyte
  esterase test on urinalysis may be due to
  urethritis rather than a UTI

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Testing for C. trachomatis

• Diagnosis of C. trachomatis urethritis in men,
  and screening in men and women
• Testing can be performed on a first pass urine
  sample (no urination for one hour prior to
  collection)
• Urethral swabbing in men or women has little
  advantage over urine testing. It may also be
  painful and poorly tolerated.
• In women endocervical swabs, high vaginal swab
  and urethral sample (either first-catch urine or
  urethral swab) will exclude most causes of
  genital tract infection.

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Positive C. trachomatis results

• If C. trachomatis infection is detected on a
  urine sample, a complete STI evaluation is
  recommended to exclude co-infection with other
  sexually transmitted bacteria, protozoa and
  viruses.

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Resources available from bpacnz on the lab
investigation of UTIs include

• Evidence based guide Laboratory Investigation of
  UTIs
• Interactive online quiz
• Quiz feedback
• UTI Clinical Audit pack for general practice
• Individual UTI investigation feedback for GPs

visit www.bpac.org.nz