Epidemiology and etiology

The prevalence and type of UTIs generally varies by age and gender.5,6 UTIs may occur at any age, even in the very young. Premature infants, for example, have a higher rate than full-term infants, and neonatal boys are five to eight times more likely to have UTIs than neonatal girls. In young children 1 to 5 years of age, significant bacteriuria occurs more in girls than boys, 4.5% compared to 0.5%, respect-

ively. Once adulthood is reached, bacteriuria increases in young, nonpregnant women (range, 1-3%), yet remains low in men (up to 0.1%).8 Symptomatic UTI affects 30% of women between 20 and 40 years of age, which represents a prevalence that is 30

times greater than men of the same age group. Upwards of 40% to 50% of the female population will experience a symptomatic UTI at sometime during their life.1

Table 79-1 Diagnostic Criteria for Significant Bacteriuria

• Greater than or equal to 10 CFU coliforms/mL or greater than or equal to

105 CFU noncoliforms/mL in a symptomatic female

• Greater than or equal to 10 CFU organisms/mL in a symptomatic male

• Greater than or equal to 105 CFU same organisms/mL in asymptomatic individuals on two consecutive specimens

• Any growth of bacteria on suprapubic catheterization in a symptomatic patient

• Greater than or equal to 10 CFU organisms/mL in a catheterized patient

CFU, colony-forming unit.

The etiology of UTIs has remained relatively unchanged over the past several decades. UTIs are either uncomplicated or complicated. There is a lack of consensus regarding the definition of what makes a UTI complicated, but in general a complicated UTI refers to a structural or functional abnormality of the urinary tract. Patients with complicated UTIs are typically given longer treatment durations than those patients with uncomplicated infections. Those with complicated UTIs by definition are also prone to more frequent infections. It is important to note that an upper UTI does not necessarily imply complicated UTI, nor does lower UTI imply uncomplicated UTI.

While the frequency of causative organisms changes depending on the location of infection and patient characteristics, over 95% of uncomplicated UTIs are the result of a single causative organism. In 85% of the uncomplicated UTI cases, the causative organism is E. coli.9 A variety of other organisms may cause uncomplicated UTIs, but represent the minority of pathogens. Other organisms include gram-positives such as Staphylococcus saprophyticus and Enterococcus spp. and gram-negative bacteria such as Pseudomonas aeruginosa, Klebsiella pneumoniae, Proteus spp., and Enterobacter spp.10-12 The chances of isolating an organism other than E. coli are higher in patients that have recurrent UTIs, particularly those patients whose UTI is considered complicated. It is also more common for organisms other than E. coli to cause UTIs in the hospitalized population than in the general population.13,14

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