The prevalence UTI varies according sex and age3. The female gender is more prone to infection for anatomical reasons: short and straight urethra and short distance between the ostium of the urethra and the anus contribute to the easy colonization of the periurethral region with enteric bacteria equipped with appropriate pili, fimbriae, etc attaching to the mucosal surface. In female the prevalence is 1% in newborns (congenital defects with functional or anatomic reflux), 4-5% in toddlers for the same reasons, 4-5%

in schoolgirls (reflux), 20% in young sexually active women (more frequent when using spermicides), 35% in middle age women (lack of oestrogen, surgery, prolapsus, incontinence, residual urine) and 40% for women >65 year for the same reasons and /or indwelling catheters and incontinence. In males the prevalence ofUTI is 1% (functional or anatomic reasons), 0.5% in preschool boys (no circumcision, sexual abuse) <0.5% from 5-35 years, 2040% and increasing with age due to prostata hyperplasia, surgery, indwelling catheters or incontinence.

The most frequent organisms causing UTI are Escherichia coli, less common are Klebsiella spp. Enterobacter spp, Proteus spp, Staphylococcus syprophyticus (women only), Pseudomonas spp, Acinetobacter spp, streptococci group B and enterococci, whereas Haemophilus influenzae, salmonella, shigella, anaerobes, yeasts or mycobacteria are rare. A clear link to UTI has not been established for Gardnerella vaginalis, Ureaplasma urealyticum and Mycoplasma hominis.

For therapeutic reasons it is useful to distinguish between uncomplicated and complicated infections. Uncomplicated infections are due to the most common microorganisms ( E. coli, klebsiellae,P. mirabilis, S. saprophyticus ) in the absence of functional or anatomical abnormalities. They are often linked to a positive personal or family history with UTI, the use of diaphragm or spermicides. This type of infection can be treated with a short course of antibiotics.

In contrast, complicated UTI, more frequently due to S. aureus or P. aeruginosa, are linked to functional or anatomical dysfunctions, to instrumentation, catheterization or to recent use of antibiotics. Risk factors for complicated UTI include males, elderly persons, previous or actual hospitalization, pregnancy, duration of symptoms > 7 days, presence of stones, indwelling catheter, recent instrumentation, anatomical abnormalities, history of UTI in childhood, immunosuppression or recent use of antibiotics. These infections need a prolonged antibiotic treatment to be cured.

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