Clinical Geriatrics

Aging is associated with a decline in function of many body systems, including the urinary tract. Bacteria seem to gain an advantage within the urinary tract of the elderly, and it is not uncommon to find bacteriuria; however, not all of these patients have a true urinary tract infection (UTI). UTI is considered to be the most common infection among the elderly^1-3 and the most common cause of bacteremia,⁴ but patients with bacteriuria who can clearly communicate the absence of urinary tract symptoms have asymptomatic bacteriuria (ASB) and do not require treatment. The prevalence of ASB increases with age, and although ASB does not directly affect the health of elderly patients, failure to recognize it as an entity separate from UTI will impact geriatric patients’ health.

Definition of Asymptomatic Bacteriuria
Bacteriuria is simply the presence of bacteria in the urine. Traditionally, UTI has been considered confirmed when the patient has a positive urine culture. Growth of bacteria in a urine culture demonstrates the presence of bacteriuria and does not give a complete picture of the patients’ health status. Those with clearly identifiable symptoms arising from the urinary tract, such as dysuria, urinary frequency, or flank pain, have a UTI. If urinary tract symptoms are absent in the elderly patient with bacteriuria, then ASB must be considered in the differential diagnosis. More specifically, ASB is the finding of 100,000 colony-forming units per milliliter (cfu/mL) of a single organism in two consecutive urine cultures obtained by clean-catch from a woman without urinary tract symptoms.5 For an asymptomatic man, the same is true except that only one positive culture is required from a voided specimen to meet the definition.5 A catheter-obtained specimen from asymptomatic men or women is ASB if 100 cfu/mL of a single organism is isolated in the urine culture.⁵ A significant proportion of the elderly with bacteriuria have ASB and not a UTI when using these definitions.

Prevalence of Asymptomatic Bacteriuria
The rate of bacteriuria occurrence increases 1-2% per decade of life,⁴ and the percentage of these with ASB also increases with age. Postmenopausal women age 50-70 have an ASB prevalence rate of 2.8-8.6%,⁵ while younger women have an ASB prevalence of 1-2%.⁶ When all geriatric age groups are combined, the prevalence of ASB in men and women living in the community is 3.6-19% and 10.8-16%, respectively.⁵ Additionally, men over the age of 80 have a prevalence rate of 20%.7 Older individuals more commonly have ASB.

The higher prevalence of ASB in the elderly correlates with general functional decline, as well as illnesses common to this group.^4,6-10 It is, therefore, not surprising that ASB is more frequently present in nursing home residents. In a group of ambulatory elderly women living in a geriatric community, ASB was shown to be related to the level of care they required.⁸ The prevalence in the women who lived in a more independent housing arrangement was 11%, but within the same community those who lived in an apartment building or a nursing home had an ASB prevalence of 18% and 25%, respectively. Eight percent of patients in nursing homes develop bacteriuria every 6 months,6 and the estimated prevalence of ASB is 25-50% for women and 15-40% for men who are institutionalized.,sup>5 Aging as well as functional decline contribute to ASB prevalence.

Pathophysiology of Asymptomatic Bacteriuria
The cause of ASB in the elderly is multifactorial, but incomplete emptying of the bladder is believed to be the primary source.^4,6,7,9,11 Bacteria gain access to the urinary tract by the ascending route from the perineum and are typically eliminated by urine flow. Impairment in this defense mechanism is the primary etiology of ASB in the elderly.