Review article
Epidemiology of urinary tract infections: Transmission and risk factors, incidence, and costs

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Uropathogenic or opportunistic?

Escherichia coli cause 80% of all community-acquired UTI among otherwise healthy individuals, and roughly half of UTI among hospitalized patients and persons with diabetes [2]. At the molecular level, E coli that cause UTI are sufficiently different from other E coli so as to be designated uropathogenic E coli (UPEC). There is some epidemiologic rationale to make this distinction: in otherwise healthy young women, a UTI caused by a pathogen other than E coli is significantly less likely to be

Risk factors

All humans are susceptible to UTI; however, certain characteristics increase exposure to potential uropathogens and others enhance susceptibility to the development of symptoms following colonization (see Fig. 1). Factors that increase exposure to uropathogens include presence of a urinary catheter and engaging in vaginal intercourse; markers of host susceptibility to disease include age; gender; and presence of underlying conditions affecting the urinary tract, such as pregnancy, diabetes, or

Asymptomatic bacteriuria

Although asymptomatic bacteriuria precedes UTI, it does not always lead to symptomatic infection. Natural history studies have demonstrated the frequent occurrence and transient nature of asymptomatic bacteriuria in women following sexual activity [9], [42], [43]. This underscores both that the bladder is an immunologic organ and that not all bacteria are equally capable of causing urinary tract disease.

Asymptomatic bacteriuria during pregnancy has been associated with progression to

Pyelonephritis

Pyelonephritis is a much less common type of UTI, but is associated with substantial morbidity and even mortality. In the United States, pyelonephritis is estimated to account for over 100,000 hospitalizations each year [53]. Cystitis very rarely progresses to pyelonephritis, although the bladder is usually also affected during kidney infection. Both host and bacterial factors influence kidney involvement: pregnancy increases the risk of movement of bacteria into the kidney, and bacteria that

Transmission

Escherichia coli are transmitted by person-to-person direct contact, and by contaminated food or water. Presumably UPEC is also transmitted by these modes, but the relative contributions of each mode are uncertain. In mouse studies, intravesical infection with UPEC leads to colonization in the gastrointestinal tract and uninfected mice in the same cage become colonized with the same strain [58]. An outbreak of UTI among paraplegic patients was caused by a single strain of Pseudomonas aeruginosa

Incidence and cost

Urinary tract infections occur frequently in people of all age groups, with an overall self-reported annual incidence of 12.1% among women and 3% among men (data from NHANES III). Peak incidence in women is age 20 to 24 at 18.6%; among men it is in the oldest age group, 85 plus at 7.3%. The estimated direct and indirect costs UTI among ambulatory women in the United States were $1.6 billion in 1995 [65].

As the most common health care–associated infection, UTI are also a significant burden on

Summary

Uropathogenic E coli have special features that allow them to take advantage of the bladder environment. There UPEC can grow to substantial numbers in pure culture that are shed frequently into the environment and have a high probability of transmission to other hosts. A better understanding of the transmission system and the host and bacterial factors influencing transmission is essential for the identification of effective prevention strategies. Although the risk of severe morbidity among

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    This work was supported in part by Grant No. R01 DK55496 from the National Institutes of Health.

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