The epidemiology of UTI varies with age and sex. There are four groups at risk for infection: neonates, girls, young women, and older men ( Fig 90.-1). In neonates, a

UTI occurs more often in males (1.5:1 M:F ratio) and is often part of the syndrome of gram-negative sepsis. The incidence of UTI in preschool children is approximately 2 percent, with the incidence in girls at least 10 times greater than the incidence in boys. In schoolage children, the incidence rises to 5 percent, almost exclusively girls.



FIG. 90-1. Natural history of urinary tract infections.

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FIG. 90-1. Natural history of urinary tract infections.

Bacteriuria is rare in males under the age of 50 and symptoms of dysuria or urinary frequency are usually due to a sexually transmitted disease-related infection of the urethra or prostate. However, in men older than 50 years, the incidence of UTI rises dramatically because of prostatic obstruction or subsequent instrumentation.

Dysuria in females is a common symptom usually due to infection. UTIs are common in otherwise healthy young women, often due to sexual contact. The incidence of infection in postmenopausal women increases with age; the prevalence of bacteriuria among elderly women in nursing homes exceeds 40 percent.

The infecting organisms are generally those found colonizing the perineum, and in women with a traditional "positive" culture of 10 5 colony-forming units (CFU) per mL of urine, Escherichia coli is responsible for approximately 80 to 90 percent of infections. However, up to one-half of cases of dysuria in young women are characterized by low bacterial colony count culture results (102 to 104/mL), which was termed the "acute urethral syndrome." It is now believed that these patients have low-grade or early urinary tract infection due to E. coli, Staphylococcus saprophyticus, or Chlamydia trachomatis. The definition of UTI based on early studies that reported only upper tract disease established that a colony count of at least 10 5/mL was necessary to indicate the presence of "significant bacteriuria." Recent research suggests that with regard to lower UTI in the presence of symptoms, a colony count of 100/mL or greater may represent significant bacteriuria and merit treatment.1

Asymptomatic bacteriuria (ABU) is defined by the presence of more than 105/mL of a single bacterial species on two sucessive urine cultures in a patient without symptoms. The requirement for two positive cultures is to eliminate those individuals with transient colonization of the urinary tract. ABU occurs in up to 30 percent of pregnant women and in up to 40 percent of female nursing-home residents. ABU is also common in patients with indwelling urinary catheters and disorders that prevent complete emptying of the bladder.

UTIs in women recur either because of relapse or reinfection. Relapse is caused by the same organism, and symptoms recurring in less than one month represents treatment failure. When symptoms recur in one to six months, it is generally due to reinfection. Reinfection is usually from a different enteric organism or a different serotype of the same organism, and may represent a defect in the defense mechanisms of the host. If a patient has a cluster of infections with more than three recurrences in one year, a more complete workup may be warranted to look for the presence of structural abnormalities, tumor, renal calculi, or associated systemic illness such as diabetes mellitus.

A UTI during pregnancy poses special problems. If untreated, ABU may progress to symptomatic UTI or pyelonephritis, especially in the third trimester, and may lead to preeclampsia, sepsis, or miscarriage. This is the single setting in which treatment of ABU is definitely indicated.

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