Urinary tract infection

Contributed by Professor Stuart L Stanton, emeritus professor of urogynaecology, St George's Hospital Medical School, London

1. Epidemiology and aetiology
Urinary tract infection (UTI) in women is common, often poorly treated, may become recurrent and can lead to serious complications.

Many infections are asymptomatic, and there is evidence that the condition is very common in the elderly.

It is particularly important to detect and correctly manage infections during pregnancy, and in children and elderly women.

About 1 per cent of boys and girls have a symptomatic UTI in their first year, rising to 2 per cent of boys and
8 per cent of girls by age seven.

Infection in women
At least 20 per cent of women aged 20–56 will have had one infection per year. The prevalence increases with age, rising to as high as 50 per cent in institutionalised populations.

Faecal bacteria from the perineum ascend into the vulva, urethra and bladder, often at the time of coitus.

The risk factors include sexual intercourse, spermicide use, frequent courses of antibiotics, low levels or lack of oestrogen affecting the quality of the urothelium, and incomplete bladder emptying, which might also  be associated with a neuropathic bladder caused by diabetes, MS or a cerebrovascular accident.

Recurrent infections are defined as occurring after the resolution of a previous UTI.

A relapsed infection involves the same organism causing another infection within two weeks of treatment.

Instrumentation of the urinary tract and foreign bodies such as catheters are also contributory risk factors to contracting an UTI.

2. Diagnosis
A UTI may present as acute cystitis or, more seriously, as acute pyelonephritis with bacteraemia and renal failure.

The classic symptoms of acute UTI include dysuria, frequency, urgency and suprapubic pain. Haematuria may be present.

In acute pyelonephritis, there may be loin pain, pyrexia and rigors.

In children, presentation may be non-specific with failure to thrive and non-specific abdominal pain. In the elderly, it is not unusual for a UTI to present as general malaise and confusion.

The patient may report cloudy and offensive smelling urine.

Examination
Examination may reveal tenderness in the suprapubic region where the infection is mostly confined to the bladder, and loin tenderness with an ascending infection. Residual urine may be present.

A dipstick test for nitrites and an esterase test for leucocytes are moderately sensitive, but there may be a high rate of false negatives, and a low-count bacteriuria will not be detected.

A positive result will allow empirical treatment to be started. If the patient has a complicated or recurrent infection, a urine sample for laboratory culture and sensitivity is mandatory. When infection is recurrent or there are associated complicating factors, such as pregnancy, or if there is a neuropathic bladder, additional tests such as a renal and bladder ultrasound scans should be carried out.

In non-pregnant patients, a plain abdominal X-ray may detect calculi. If there has been significant haematuria, a cystoscopy may be necessary.

Differential diagnosis
Many conditions can mimic UTI, including interstitial cystitis (presenting as frequency and pain), endometriosis and pelvic inflammatory disease.

Drug-induced cystitis can occur with NSAIDs, gemfibrozil and simvastatin. The time interval between drug-taking and presentation may be several years, so a careful history and a high index of suspicion are necessary. Anxiety can cause symptoms of frequency and urgency that may resemble a UTI.

Other conditions that may confuse the diagnosis are radiation cystitis, carcinoma in situ and bladder tumour.

Any woman over 50 who has persistent urgency, frequency and dysuria without evidence of bacteriuria on MSU should have urine cytology.

The urethral syndrome is a diagnosis of exclusion defined as irritative bladder symptoms (suprapubic discomfort, urinary frequency, urgency and burning) in the absence of any objective urological findings.

A urethral swab should be taken to exclude chlamydial or gonococcal infection.

3. Treatment and prevention
Because UTIs occur frequently, many women turn to alternative medicines.

It is useful to advise the patient about simple measures including drinking two litres of fluid a day, and regular three-hourly voiding with complete bladder emptying.

Treatment
Antimicrobials should be started when symptoms are present.

Trimethoprim over five days is effective for about 70 per cent of common urinary pathogens. It is not effective against infections due to pseudomonas or enterococci.

Nitrofurantoin four times a day for seven days is another first-line choice, but should be used with caution in the elderly because of the risk of impairment of lung, hepatic or renal function.

Cephalosporins are excreted in high concentrations in the urine, but there is a cross reactivity to these drugs in patients with penicillin allergy. They may also cause candidiasis in about 15 per cent of women.

In proven pseudomonas and enterococcal infections, the quinolone antibiotics such as ciprofloxacin, norfloxacin or ofloxacin are indicated.

Tetracyclines, quinolones and nitrofurantoin should be avoided in pregnancy. Trimethoprim is an anti-folate agent, so should also be avoided in early pregnancy while neural tube development is occurring.

The length of treatment is contentious. One- to three-day courses are convenient and less expensive, but may result in more recurrent infections.

Referral is advised if symptoms frequently recur or become chronic, or if there is painless haematuria, and if the patient has diabetes, a neuropathic bladder, is pregnant or has pyelonephritis.

Prevention
A number of preventive options are available. Cranberry juice has been known to many generations of North Americans as an aid in managing urinary infection, and it has been shown to have an anti-adhesion effect that prevents E coli from adhering to the urogenital tract.

A twice-daily regimen of 300ml cranberry juice, or the equivalent in a powder or capsule, can be recommended as a preventive.

The French public institution for food safety recently approved the use of cranberry ingredients for the prevention of UTIs. There has been recent concern about an interaction between cranberries and warfarin leading to raised INR.

To be safe, any patient on warfarin should inform their anticoagulant clinic or healthcare adviser before changing the amount of cranberry juice they are taking.

Cranberry juice should not displace antibiotics when treatment is needed, but may be a useful adjunct to treatment in high-risk groups.

It is advisable to avoid spermicides, diaphragms and spermicide-containing condoms in cases of recurrent infection. However, there is little evidence to support personal hygiene precautions such as always wiping the vulva from front to back, or using specific types of underwear or soaps. Evidence is also weak that post-coital voiding of urine is of much benefit.

Infection susceptibility
Oestrogen replacement is helpful in post-menopausal women where increased susceptibility to infection may be due to changes in the vaginal flora and the urothelium. Several preparations may be used, including oestrogen-containing creams.

Antimicrobial prophylaxis can be taken either as a single post-coital dose, or as a course of low-dose antimicrobials for six to 12 months.

Vaccines are currently being developed against the causative bacteria.

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