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.
The laboratory investigationof urinary tract infections
Uncomplicated vs complicated UTI
When is urine culture not helpful?
When is urine culture helpful?
Testing for asymptomatic bacteriuria
Chlamydia trachomatis urethritis
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
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 infectionif patients present with symptoms of a UTI + suspicious sexual history
Complicated UTIs are those occurring in…
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%.
Urine culture should be performed for:
Women with a UTI with complicating features
All pregnant women
Men with suspected UTI
Suspected acute pyelonephritis
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.
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
All UTIs in men are considered complicated, therefore a urine culture is indicated, even if the urine dipstick is negative.
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
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.
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.
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.
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.
All in-dwelling catheters eventually become colonised with bacteria.
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.
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
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.
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.
Evidence based guide ‘Laboratory Investigation of UTIs’
Interactive online quiz
UTI Clinical Audit pack for general practice
Individual UTI investigation feedback for GPs