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Chapter: Medicine and surgery: Genitourinary system

Urinary tract infections (UTIs) - Urinary tract infections

An infection of the urinary tract which may be further distinguished on the basis of anatomy, e.g. cystitis, pyelonephritis. In females, vaginitis is another syndrome which commonly overlaps. - Definition, Incidence, Aetiology, Pathophysiology, Clinical features, Complications, Investigations, Management, Prognosis.

Urinary tract infections


Urinary tract infections (UTIs)




An infection of the urinary tract which may be further distinguished on the basis of anatomy, e.g. cystitis, pyelonephritis. In females, vaginitis is another syndrome which commonly overlaps.




All ages




> M




Most frequently due to bacteria, in particular E. coli and Proteus mirabilis. Hospital acquired infections may be due to other organisms such as Staphyloccoccus, Enterococcus and Klebsiella. Less commonly, fungi (Candida and Histoplasma capsulatum), parasites (the protozoan


Trichomonas vaginalis and the fluke Schistosoma haematobium) and very rarely viruses can cause UTIs.




Bacterial virulence factors: Critical to the pathogenesis of bacteria is adherence to the uroepithelium as infections ascend from the urethral orifice to the bladder and to the kidney in pyelonephritis. E. coli have special fimbriae (also called pili) which permit adhesion. Other virulence factors include flagellae (to permit mobility), production of enzymes such as haemolysin (E. coli and Proteus) which induces pore formation in cell membranes. E. coli also inhibits phagocytosis. Urease is produced by some organisms (e.g. Proteus), it hydrolyses urea and increases ammonia, which facilitates bacterial adherence.


Host predisposing factors include any functional or anatomical abnormality of the urinary tract such as urinary stasis, reflux or stones. Other important risk factors include sexual intercourse, diabetes mellitus, immunosuppression, instrumentation (including catheterisation) and pregnancy.


Urine itself is inhibitory to the growth of normal urinary flora (non-haemolytic Streptococcus corynebacteria, Staphylococcus) through its pH and chemical content.


Clinical features


Acute cystitis typically presents with dysuria (a burning pain on passing urine), urgency and frequency. Fever and other systemic features are variable. Macroscopic haematuria is not uncommon, although this should prompt further investigation for any other underlying disease such as urinary stones or a bladder malignancy. Pyelonephritis may present with few lower urinary tract symptoms, but more commonly causes systemic upset with fever, rigors, chills, and loin pain or tenderness. Pro-statitis causes fever, malaise and pain in the perineum and lower back as well as dysuria and frequency. Both pyelonephritis and prostatitis may be due to ascending or haematogenous infection (usually ascending).


·        UTIs in pregnancy, the elderly and those with indwelling catheters may be asymptomatic, or may present nonspecifically with fever, falls, vomiting, or confusion etc.




The urine is cloudy due to the pyuria (pus cells) and bacteriuria, and may contain visible amounts of blood (macroscopic haematuria). Sterile pyuria (pus cells without a positive culture) may be caused by antibiotic treatment, stones, drugs such as NSAIDs and occasionally tuberculosis.




Recurrent infections which may be relapses or a reinfection. Over time, recurrences can cause chronic inflammatory changes in the urinary tract (bladder, prostate).

Urinary stones for example, Proteus, through the production of urease, causes the alkalinisation of urine, so that phosphate, carbonate and magnesium are more likely to precipitate to form struvite stones.


Bacteraemia can lead to septicaemia and in vulnerable hosts, infective endocarditis.




Mid-stream urine for urinalysis (dipstick testing), microscopy, culture and sensitivity. A culture is regarded as positive if >105 of a single organism per mL.


Patients with systemic symptoms should have a blood culture, FBC and differential, U&Es and creatinine to look for dehydration and any evidence of renal impairment. Further investigations are required in children, males and females with recurrent infections.




Empirical antibiotic therapy is used in symptomatic patients, until culture and sensitivity results are available. Uncomplicated cystitis in a woman usually only requires 3 days of oral antibiotics, whereas longer courses are required in complicated cases, e.g. those with urinary stasis, indwelling catheters, pyelonephritis and prostatitis. Intravenous antibiotics should be used in those who are systemically unwell or those who are vomiting.


·        Commonly used drugs include trimethoprim, amoxycillin and co-amoxiclav (as many infections are caused by β-lactamase producers). Quinolones such as ciprofloxacin are useful as resistant E. coli and Proteus are uncommon, but they do not adequately cover grampositive organisms.


·        Intravenous therapy is often with a cephalosporin with or without gentamicin.


Oral fluids should be encouraged where possible to prevent dehydration and relieve symptoms. Cranberry juice may also have a role in reducing symptoms, but has not been shown to be effective in treatment or prevention of UTIs.


Recurrent UTIs may be reduced, e.g. by passing urine after intercourse, treatment of stones and in some cases prophylactic antibiotics. These may cause microbial resistance, and some centres advise a ‘cycling regime’, e.g. of three different antibiotics, each used for 1 month to prevent this.

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