Urinary tract infections

Published on 11/04/2015 by admin

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Last modified 11/04/2015

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Urinary tract infections

Introduction

Urinary tract infections are a common problem in surgery. They may be responsible for urinary tract symptoms presenting to a clinician for diagnosis or for abdominal pain that is not obviously urological. More often, urinary tract infections are a secondary problem. They can occur after operation, particularly if a urinary catheter has been employed, or may complicate surgical disorders of the urinary tract such as tumours or stones. Most infections are caused by common bacteria of faecal origin.

Urinary tract infections may also be caused by unusual organisms, in particular Mycobacterium tuberculosis. On a worldwide basis, other organisms are more important causes of infection, notably the trematode Schistosoma. One variety causes severe bladder disease in some developing countries.

Urethral infections are usually transmitted by sexual intercourse. Gonococci and Chlamydia are most commonly involved. A late result of gonorrhoea in males may be a fibrous urethral stricture. Urethral strictures are covered in this chapter, although most are traumatic and not infective in origin.

Bacterial infections of the lower urinary tract

Pathophysiology of lower urinary tract infections

Common urinary tract infections caused by faecal organisms involve the bladder, the upper tract (kidney, pelvicalyceal system and ureter) or both. The bladder is infected most often, with females being particularly susceptible. Probably half of all females are affected at some time. Infection rate rises with pregnancy and with increasing age. In females, the infecting organisms probably enter via the urethra, which is only 3 cm long. Organisms easily spread from perineal skin, particularly during sexual intercourse.

Normally, the bladder is flushed clean by the frequent passage of newly produced urine, preventing multiplication of bacteria. Stasis—such as incomplete bladder emptying, dehydration or immobility—interferes with this mechanism and predisposes to infection. Urethral instrumentation greatly predisposes to infection in either gender.

Clinical features of lower urinary tract infections

Typical symptoms of bladder infection are dysuria, frequency, urgency and a sensation of incomplete bladder emptying. The term ‘cystitis’ is often used by patients to mean symptoms in this list; however, infection is not always involved and the term is best avoided. Even when infection is present, symptoms may be trivial or absent, making diagnosis difficult. Abdominal pain may be the only symptom so most patients with abdominal pain should have urine tested as a matter of course.

There are often no localising symptoms in the elderly or the very young, and the patient may be non-specifically unwell. In any ill patient in these age groups, urine must be sent for examination before antibiotics are given. Recurrent fever in a child can result from urinary infection. A sudden onset of enuresis or urinary incontinence in children or the elderly should also suggest bladder infection. Presentations of bladder infection are summarised in Box 38.1.

Box 38.1   Presentations of bladder infection

Bacteriological diagnosis of lower urinary tract infections

Urinary tract infection is confirmed by examining a ‘midstream’ specimen of urine (MSU). If the specimen cannot be examined quickly, it should be refrigerated or it rapidly loses its diagnostic value. The specimen is examined microscopically for white blood cells (‘pus cells’) and bacteria, and cultured to identify the organism and determine antibiotic sensitivity. Bacterial contamination is common; a ‘significant’ infection is therefore defined as one with abundant pus cells (more than 100 000 (105) organisms per ml). Enteric organisms are almost always responsible, the usual culprits being Escherichia coli, Proteus spp., Enterococcus faecalis and Pseudomonas (the last in debilitated or catheterised patients). Staphylococcus saprophyticus is an important cause of uncomplicated bladder infection in young sexually active females.

Significant pus cells without bacterial growth most often result from patients taking antibiotics. If not, a stone, tumour, prostatitis or tuberculosis must be suspected and investigated. Infection often causes frank or occult haematuria but only warrants investigation if it persists after treating the infection. It must be noted that up to 10% of patients with infection have an underlying bladder cancer.

Some females experience symptoms typical of urinary infection but no evidence of bacterial infection of urine is found despite multiple MSUs. Non-specific urethral inflammation from the trauma of intercourse may be responsible (the ‘urethral syndrome’).

Management of bladder infections

Antibiotic therapy is the treatment for bladder infection, chosen on a ‘best-guess’ basis if treatment is urgent and changed if necessary. Treatment should be commenced only after an MSU specimen; this should be repeated if antibiotic treatment is ineffective or in complicated cases.

Patients who have had urinary tract infections should be encouraged to increase fluid intake. This is often effective with early or mild symptoms and probably allows mild infections to resolve without drugs.

In pregnancy, ureters and renal pelvis dilate under the effect of progestogens and become more susceptible to infection. Where bladder infection is suspected, significant bacterial growth should be treated with appropriate antibiotics, whether or not the patient is symptomatic. This is because of the risk of infection ascending to upper tracts and subsequent miscarriage. The antibiotic must be safe for use in pregnancy and non-teratogenic, e.g. a cephalosporin. Trimethoprim is also safe but may deplete folate. Standard texts such as the British National Formulary should be consulted on prescribing in pregnancy.

Recurrent bladder infections

Patients likely to suffer recurrent infections tend to fall into three groups:

Patients with urinary tract abnormalities predisposing to infection

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