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The laboratory investigation of urinary tract infections. 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. Contents.
Screening for asymptomatic bacteriuria is not recommended except in pregnant women
Chlamydia trachomatis urethritis can cause similar symptoms to a UTIKey messages
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 infectionif patients present with symptoms of a UTI + suspicious sexual historyIntroduction
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%.Urine culture is not helpful for women with uncomplicated lower urinary tract infections as it does not improve outcomes.
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.Complicating features in women include:
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 pregnancyUrine culture is recommended for pregnant women
Antibiotics should be commenced while waiting for culture results
Post-treatment urine cultures are recommended one to two weeks after antibiotic therapyA urine culture is indicated when acute pyelonephritis is suspected
Urine culture should be performed
If urine culture is negative, STIs (C. trachomatis, N. gonorrhoea) should be excluded.
Gram-negative bacilli are most common cause, but enterococci and Chlamydia have been associated with chronic infection.
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.
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.
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.
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 UTIChlamydia trachomatis urethritis
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.Testing for C. trachomatis
Interactive online quiz
UTI Clinical Audit pack for general practice
Individual UTI investigation feedback for GPsResources available from bpacnz on the lab investigation of UTIs include: