The laboratory investigation of urinary tract infections

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

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 Contents

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 Contents

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 Contents

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.

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

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%. Contents

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 Contents

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. Contents

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 Contents

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. Contents

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 Contents

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. Contents

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. Contents

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. Contents

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. Contents

Regular urine culture or dipstick testing is not indicated for people with in-dwelling catheters All in-dwelling catheters eventually become colonised with bacteria. Contents

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. Contents

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 Contents

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. Contents

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.

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