Urinary Tract Infection Syndromes: Occurrence, Recurrence, Bacteriology, Risk Factors, and Disease Burden

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Key points

  • The bladder is continuously invaded by bacteria, which can grow to substantial numbers before spontaneous clearance.

  • Host factors, host behaviors, and bacterial characteristics are risk factors for the development of symptoms.

  • Urinary tract infection (UTI) occurs more often in females than in males.

  • Except during pregnancy, asymptomatic bacteriuria is not a treatable condition.

  • Cystitis and pyelonephritis are likely to recur, regardless of age, gender, or treatment.

  • The gram-negative rod Escherichia

Disease description

Urinary tract infection (UTI), an infection anywhere in the urinary tract (urethra, bladder, ureters, or kidneys) is very common. In 2007 in the United States there were 10.5 million ambulatory visits for UTI, accounting for 0.9% of all ambulatory visits.1 Almost one-fifth (21.3%) of these visits were to hospital emergency departments. UTI is among the most common primary diagnoses for United States women visiting emergency departments.2 Prevalence of UTI is high among inpatients also: in a

UTI syndromes and their occurrence: asymptomatic bacteriuria, cystitis, pyelonephritis, and catheter-associated UTI

The urinary tract has a portal to the outside, making it particularly susceptible to invasion by microbes. Bacteria normally inhabit the tissues around the urethral opening, and frequently colonize the urine. Among men, culture of a random initial void will find 1% to 5% colonized with Escherichia coli; urethral colonization is higher among men whose female sex partner has a UTI.4 Among women, urinary colonization rates are higher; the vaginal cavity and rectal opening are close to the urethral

Recurrence

UTI has a propensity to recur with a frequency that varies by population (Table 2). Among children younger than 16 years with UTI participating in UTI intervention trials in Australia and Finland, the risk of recurrence within 1 year was 19% to 22%.25, 26 The risk of recurrence is even higher among sexually active young women. In a Michigan study following 285 college women with first UTI for 6 months, the risk of a second was 24% within 6 months.27 In a Seattle study of 796 women starting a

Bacteriology

Urine is a good medium for bacterial growth, so it is not surprising that many bacteria can grow in the urinary tract, and do so frequently (Box 1, Fig. 2). The bacteria colonizing the urinary tract do not cause disease in most cases because the host has many effective methods for rapidly removing bacteria from the system. These methods include urination and innate and adaptive host immune response. Bacteria that do cause UTI either have special features that enable them to survive in the

Risk factors

Risk factors for UTI (Box 2) can be divided into factors that expose the host to potential uropathogens, those that enhance colonization by the uropathogens, and those that lead the host to respond to colonization causing diseases (see Fig. 2). Uropathogens live in multiple environments, including the bowel, periurethral area, vaginal cavity, and urinary tract; they are transferred between individuals via person-to-person direct contact, including sexual activity, and via the fecal-oral route.

Disease burden

The vast majority of UTIs are confined to the bladder (Box 3). Typical symptoms are hematuria, dysuria, urgency, frequency, nocturia, offensive smell, and abdominal pain. In a study of 684 women aged 18 to 70 years with UTI, participants reported an average of 3.83 symptom days, 2.89 restricted-activity days, and 3.13 days during which they were unwell. Most symptoms lasted no more than 3 days, with hematuria having the shortest duration (1.88 days) and urinary frequency the longest (3.14 days).

Summary

  • The bladder is continuously invaded by bacteria, which can grow to substantial numbers before spontaneous clearance.

  • Host factors, host behaviors, and bacterial characteristics are risk factors for the development of symptoms.

  • UTI occurs more often in females than in males.

  • Except during pregnancy, ASB is not a treatable condition.

  • Cystitis and pyelonephritis are likely to recur, regardless of age, gender, or treatment.

  • The gram-negative rod E coli is the most common cause of UTI in all settings,

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