Please note: In 2003, the CTF updated its Grades of Recommendations to include an "I Recommendation" for situations where insufficient evidence exists to allow a recommendation to be made.  (Formerly, these situations were captured under a "C Recommendation".)  This change is not retroactive, and all "C Recommendations" made prior to 2003 have not been reevaluated in light of the new "I" recommendation grade.  For a discussion of these recommendation grades, please link to the 2003 article in the Canadian Medical Association Journal here.

Screening for Asymptomatic Bacteriuria in the Elderly

Overview
The proportion of the Canadian population which is elderly will continue to increase over the next several decades. A high proportion of these elderly individuals will reside for at least some time in a long-term care facility. There is a marked increase in prevalence and incidence of bacteriuria in older populations. Most of this bacteriuria appears to be asymptomatic. For the institutionalized elderly with multiple co-morbidities and substantial functional impairment the prevalence of bacteriuria is extremely high. It has been argued that bacteriuria in the elderly, particularly associated with pyuria, which is evidence for a host response, should be treated. Identification and treatment of asymptomatic bacteriuria, however, would require repeated screening of elderly populations and intense antimicrobial exposure. In 1979 the Canadian Task Force on the Periodic Health Examination found that there was fair evidence that routine screening for urinary tract infection not be included among conditions sought in a periodic health examination.< 1,2>

Burden of Suffering
Population studies in women report a prevalence of bacteriuria of 2-4% among sexually active young women which increases to 6-8% in women aged 60 years, and over 20% in well elderly women in the community over 80 years.<3> Bacteriuria is uncommon in younger male populations, with a prevalence of less than 1% until about age 60 years. From 1-3% of men aged 60-65 will have bacteriuria, and the prevalence increases to 10% or more for men over age 80 years.<3> The prevalence of bacteriuria is extraordinarily high for the more impaired elderly with functional deficits and co-morbid illnesses who require institutional care. Studies consistently report a prevalence of bacteriuria from 30-50% for institutionalized women and 20-30% for institutionalized men.<2> Limited studies also suggest a high incidence of bacteriuria for the institutionalized and ambulant elderly.<3,4>

Bacteriuria in the elderly is usually asymptomatic. Morbidity with asymptomatic bacteriuria may include short-term complications of acute symptomatic infection and potential long-term complications of renal failure or mortality. Measuring the burden of illness potentially related to asymptomatic bacteriuria in the elderly is, however, limited by several factors. First, no population-based studies in the ambulatory elderly document the occurence and impact of symptomatic urinary infection. Second, chronic genitourinary symptoms are frequent in the elderly population. Such symptoms are not ameliorated by treatment of associated asymptomatic bacteriuria and occur with equal frequency in bacteriuric and nonbacteriuric elderly populations.<5> Thus, while not due to bacteriuria, they may complicate the identification of symptomatic infection. Finally, the multiple co-morbid illnesses and functional disability of the elderly institutionalized population leads to impaired communication and identification of symptomatic infection.

Limited reports document the frequency of symptomatic infection in elderly populations. Boscia et al reported 10 of 61 elderly ambulatory women with untreated asymptomatic bacteriuria became symptomatic during 6 months of follow-up, an incidence of 0.9/1000 patient days.<6> Mims et al followed 238 elderly men from 1 to 4.5 years, 29 of whom were initially bacteriuric and 17 of 134 who were followed for one year or more who subsequently became bacteriuric.<7> Only 5 patients of the initial bacteriuric group became symptomatic and they were apparently treated with antimicrobial therapy with resolution and without further complication. In 50 elderly institutionalized women with asymptomatic bacteriuria, half of whom were treated, 4 episodes of symptomatic infection occurred in one year of follow-up, an incidence of 0.26/1000 patient days.<8> In 36 elderly institutionalized men with asymptomatic bacteriuria followed for a mean of 10.6 months, 16 of whom were treated with antimicrobials, 4 episodes of symptomatic infection or 0.34/1000 patient days developed.<9>

Urinary infection is the most common cause of bacteremia in both institutionalized and noninstitutionalized elderly populations.<3,4> Women over age 65 with acute non-obstructive pyelonephritis are more likely to be bacteremic than younger women. The case fatality rate associated with bacteremic urinary infection in the elderly has been reported to be from 10-30%. Despite these observations urinary infection is rarely a direct cause of death in elderly subjects.<3,4>

Several other clinical presentations in the elderly are frequently attributed to urinary infection because of the difficulty in ascertainment of symptoms and high prevalence of bacteriuria in this population. Where specific symptom presentations other than pyelonephritis or lower tract irritative symptoms have been critically studied, however, urinary infection has not been documented to be an important contributor to such symptoms. For instance, gross hematuria is seldom attributable to hemorrhagic cystitis in institutionalized elderly subjects despite a high prevalence of bacteriuria in residents with gross hematuria.<10> Limited studies suggest that nonspecific changes in clinical status in the absence of fever are not attributable to urinary infection.<11> The majority of febrile episodes of uncertain cause in the non-catheterized bacteriuric elderly are likely not caused by invasive urinary infection, although the contribution of urinary infection in an individual case may be impossible to ascertain.

The contribution of asymptomatic bacteriuria to mortality in the elderly has been controversial. Initial studies from Finland<12> and Greece<13> suggested decreased survival in both women and men with asymptomatic bacteriuria. Subsequent studies in community populations from Sweden<14> and Finland<15> have not supported these initial observations. No association of bacteriuria with mortality has been reported for the institutionalized population.<16> Currently evidence does not support a direct or indirect causal association of asymptomatic bacteriuria with mortality in elderly populations. In addition, there is no evidence that asymptomatic bacteriuria, by itself, progresses to renal failure in this population.

Maneuver
Screening by culture or non-culture (e.g. leukocyte esterase/nitrate dipstick) methods of urine of asymptomatic elderly subjects to identify bacteriuria with subsequent antimicrobial treatment of bacteriuria.

Effectiveness of Prevention and Treatment

Ambulatory Elderly
Boscia et al<5> studied 124 non-institutionalized ambulatory elderly women and reported that identification and treatment of asymptomatic bacteriuria decreased the frequency of symptomatic episodes from 16% to 8% in the subsequent 6 month period. The type of symptom presentation was not described. This difference was not statistically significant. The prevalence of bacteriuria at 6 months after treatment was 64% in the non-treated group and 35% in those who were treated. Mortality for the treated (3.2%) and untreated (4.9%) groups was not different (p=0.66). Cost analysis was not performed.

No prospective, randomized study of therapy vs. no therapy for asymptomatic bacteriuria in the non-institutionalized elderly male has been reported. One prospective cohort study provides limited data describing morbidity.<7> In this study, 234 elderly men were followed for up to 4.5 years, 134 for over one year. Twenty-nine were bacteriuric at initial screening and 20 became positive in follow-up. The majority (76%) of bacteriuric subjects spontaneously cleared bacteriuria after a mean period of 4.4 months (range 3-12 months). Only 5 (17%) bacteriuric subjects were treated for symptomatic infection and bacteriuria recurred rapidly during post-treatment in 3 of these 5. The symptom presentations were not described, and no significant detrimental outcomes with development of symptomatic infection were reported. This study suggested a high frequency of spontaneous resolution of asymptomatic bacteriuria in elderly non-institutionalized men and a low frequency of symptom development. It was concluded that screening for and treatment of asymptomatic bacteriuria was not warranted in ambulatory elderly men.

Institutionalized Elderly
Prospective, randomized studies in institutionalized women<8> and men<9> have documented no benefits of screening for and treatment of asymptomatic bacteriuria. In 36 institutionalized elderly men randomized to treatment or non-treatment and followed for 2 years, subsequent symptomatic episodes occurred with equal frequency in treated or non-treated subjects.<9> Mortality was 5 (31%) in treated and 5 (25%) in untreated subjects. In 50 institutionalized elderly women randomized to treatment or no treatment and followed for one year, morbidity from urinary infection was similar in treated and non-treated groups.<8> Antimicrobial therapy, however, was associated with significantly more adverse medication effects, increased reinfections, and a tendency to emergence of resistance. Mortality was 4 (18%) for untreated and 9 (39%) for treated subjects. Thus, these studies in the institutionalized elderly support the non-treatment of asymptomatic bacteriuria.

One characteristic of the institutionalized bacteriuric elderly is the rapid recurrence of bacteriuria following antimicrobial therapy.<8,9> In most individuals, treatment of asymptomatic bacteriuria is followed by an extremely short period free of bacteriuria, with over 50% recurring within 2-4 weeks of discontinuing antimicrobials. In institutionalized women with urine cultures obtained monthly, screening and antimicrobial treatment of all identified episodes decreased the overall prevalence of bacteriuria in the population by only 30% over a one year period.<8> Thus, for the institutionalized population, even intensive antimicrobial therapy for asymptomatic bacteriuria has limited impact on bacteriuria. Even if benefits of treatment of asymptomatic bacteriuria in the elderly were identified, frequent repeated screening for urinary infection would be required.

Subjects with long-term indwelling catheters are virtually always bacteriuric. Screening for bacteriuria or pyuria in these subjects will not identify those at risk for morbidity.<17> Antimicrobial therapy of asymptomatic catheter-acquired bacteriuria does not decrease morbidity from urinary infection, but will lead to emergence of organisms of increased resistance.<18>

Recommendations of Others
The recommendations of the U.S. Preventive Services Task Force on screening for asymptomatic urinary tract infection are currently under review. Other authors<19> have suggested there is no indication for screening for or treatment of asymptomatic bacteriuria in elderly populations.

Conclusions and Recommendations
There is no evidence that treatment of asymptomatic bacteriuria in elderly populations is beneficial. Treatment of asymptomatic bacteriuria will not decrease the frequency of symptomatic episodes or alter outcomes in institutionalized populations and may be associated with an increased occurence of resistant organisms. For the non-institutionalized elderly, while there may be some small decrease in the occurence of symptomatic infection, the data do not indicate sufficient impact to suggest that it would be cost effective. For men, the lack of evidence for short- or long-term adverse outcomes in those with asymptomatic bacteriuria suggests that treatment would not be indicated, although comparative randomized trials are not available for this group. Thus, there is good to fair evidence not to screen elderly populations for the presence of asymptomatic bacteriuria (D and E Recommendations depending upon subgroup). However, for ambulatory elderly women, specifically, there is insufficient evidence to recommend for or against screening (C Recommendation).

Unanswered Questions (Research Agenda)
The following have been identified as research priorities:

1. Population based studies documenting the impact of morbidity from symptomatic urinary infection in non-institutionalized elderly women and men.
2. Defining the clinical significance of a positive urine culture in ambulatory elderly men as it relates to prostatic obstruction or other genitourinary abnormalities.
3. Contribution of bacteriuria to episodes of fever in the institutionalized elderly with a positive urine culture.

This review was initiated in June 1993 and recommendations were finalized by the Task Force in October 1993.

Full Citation
Nicolle L.E. Screening for asymptomatic bacteriuria in the elderly. In: Canadian Task Force on the Periodic Health Examination. Canadian Guide to Clinical Preventive Health Care. Ottawa: Health Canada, 1994; 966-73.