Family Practice Advance Access originally published online on April 4, 2006
Family Practice 2006 23(3):303-307; doi:10.1093/fampra/cml007
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Asymptomatic bacteriuria in a population of elderly residents living in a community setting: prevalence, characteristics and associated factors
a Centre for Clinical Research, Dalarna, Uppsala University Uppsala, Sweden
b Unit of Research and Development in Primary Care, Jönköping, Uppsala University Uppsala, Sweden
c Department of Public Health and Caring Sciences, Family Medicine and Clinical Epidemiology Section, Uppsala University Uppsala, Sweden
Correspondence to Dr Nils Rodhe, Centre for Clinical Research, Nissers väg 3, SE-791 82 Falun, Sweden; Email: nils.rodhe{at}ltdalarna.se
Received 17 September 2005; Accepted 8 March 2006.
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Abstract |
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Background. Asymptomatic bacteriuria (ASB) is common among the elderly in institutional care, but less is known about its prevalence among the elderly living in community settings. Knowledge of the prevalence of ASB in this population could contribute to a reduction in unnecessary use of antibiotics.
Objective. To study the prevalence of ASB and associated health and social factors in a population of elderly people, aged 80 and over, in a community setting.
Design. A cross-sectional study.
Setting. The catchment area of a primary health care centre in a Swedish middle-sized town.
Method. All residents, aged 80 and over, except for those in institutional living, were invited. A structured interview was carried out and urinary culture obtained.
Results. ASB was found in 14.8% of the participants, in 19.0% of the women and 5.8% of the men. In women independent associations with ASB were found for urinary incontinence (OR: 2.99, CI: 1.60–5.60), reduced mobility (OR: 2.68, CI: 1.42–5.03) and oestrogen treatment (OR: 2.20, CI: 1.09–4.45).
Conclusion. Bacteriuria is common among the elderly living in non-institutional community settings, especially among women, although not as common as among the elderly in institutional settings. A woman over 80, with urinary incontinence, and needing support to walk has a risk of nearly 50% of presenting with ASB, a condition about which there is consensus not to treat with antibiotics. This should be borne in mind when examining patients with diffuse symptomatology and an accidental finding of bacteriuria.
Keywords. Aged, bacteriuria, epidemiology, incontinence, urinary.
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Introduction |
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Antibiotic treatment is relatively frequent among the elderly and increases with age.1 In institutional care for the elderly in Sweden, urinary tract infections are the reason for more than half of the antibiotics prescribed.2 Increasing occurrence of antibiotic resistance, especially among the elderly in institutional care, has highlighted the importance of reducing unnecessary use of antibiotics.
The prevalence of asymptomatic bacteriuria (ASB) is quite well described among the elderly in institutional care, varying between 15 and 30% in men and 25 and 50% in women.3,4 Only a few investigations have focused on the elderly living in community settings. These show that the prevalence of ASB among ambulatory women increases from <5% in middle age to 
10% in the age of 70 and 20% in the age of 80. Among men the prevalence up to middle age is 1% and then increases to 5–10% in the age of 80,4,5 a major predisposing factor presumably being prostatic disease.6
The high prevalence of bacteriuria among the elderly in institutional care is linked to impaired functional status and urinary incontinence.7 It has not been fully investigated whether this is also true for elderly people living in community settings.
The aim of this study was to describe the prevalence of ASB and health-related factors among elderly residents in the community and to describe the urinary tract bacteria found in this population.
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Material and methods |
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Study population
The study was carried out in the geographical catchment area of Britsarvets primary healthcare centre in Falun, a municipality in the county of Dalarna, Sweden, during the period of March to June 2003. Falun is a town of 55 000 inhabitants, 16.8% of whom are 65 years or older. Socio-economic factors such as mean income from work, proportion of population employed and costs per capita for the elderly in Falun are close to the average in Sweden.8 The catchment area includes a total of 12 000 inhabitants residing in both residential areas and apartment houses. There are also three blocks of service flats for the elderly or disabled. In these blocks there is a nurse available during the daytime, but the residents live in their own apartments with the possibility of having their meals in a common dining room. All registered residents in the catchment area, not living in an institution, aged 80 and over (642 subjects) were identified, but before the investigation was carried out 48 had moved out and 17 had died, making the eligible number of subjects 577. Of these, 30 (5.2%) were excluded who were not able to provide a specimen due to dementia and/or incontinence. Nine (2%, all of them men) who had an indwelling catheter and one woman who was diagnosed as having a symptomatic urinary tract infection at the time of investigation were also excluded.
Urine specimens
Possible participants were sent an information letter and then within a week contacted by a specially trained study nurse, and if giving consent, a home visit was arranged.
At the home visit, a specimen was obtained by requesting the participant to collect a urine sample in a clean container. The specimens were transported refrigerated to the local microbiology laboratory. Quantification, identification and susceptibility testing of organisms were performed on CLED-agar according to Swedish standards. If this first culture was positive a second, confirming, specimen was taken within 1–2 weeks. A positive culture was defined as growth of >108 cfu/l. ASB was defined as the growth of >108 cfu/l of the same species of bacteria in two consecutive urine specimens in the absence of new, obvious symptoms from the urinary tract. Cultures with a mixed flora or a growth of <108 cfu/l were regarded as negative.
Questionnaire
The study nurse interviewed all participants and filled in the questionnaire. If necessary, close relatives and nursing staff were also used as informants. Supplementary information was obtained from medical records when needed. The questionnaire gave data about accommodation, diabetes mellitus, stroke, prostatic disease, oestrogen and diuretic treatment, mental status, functional independence, mobility, urinary incontinence, symptoms from the urinary tract and whether antibiotic treatment had been given in the previous 3 months. Diabetes was defined as having tablet or insulin treatment for diabetes, and prostatic disease as being on medication for prostatic disease or having a history of prostatic surgery. Oestrogen treatment included local and/or systemic treatment. Urinary incontinence was defined as respondents complaining of involuntary urinary leakage at least once a week.
Measurements of health indicators
Mental status was measured by the mini-mental state examination (MMSE)9 and reduced mental status was defined as having an MMSE score <24. Functional status was measured by the Katz index of activities of daily living and reduced functional status was defined as need of assistance in at least one activity (bathing, dressing, toileting, transfer, continence or feeding, Katz index A + B). Reduced mobility was defined as not being able to walk indoors without support (other than a stick).
Statistical analysis
Software used was JMP® 4.0.2 of the SAS System for windows. Copyright © 1989–2000 SAS Institute Inc., Cary, NC, USA. Proportions were compared using chi-square test and logistic regression technique was used to determine the independent factors associated to ASB and to create the regression surface in Figure 1.
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Results |
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Of the 537 elderly individuals invited to participate, 105 (19.6%) did not agree to participate. The only factor that distinguished those who did not agree to participate from the others was that fewer of them lived in the blocks of service flats (Table 1).
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The characteristics of the studied population (n = 432) are shown in Table 2. Mean age was 84.7 years, 294 (68%) were women and 62 (14%) were living in service flats. Diabetes was reported by 10% of the participants, urinary incontinence by 30%, reduced mobility by 25% and 4.7% had the combination of reduced mobility and a history of stroke.
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The first culture was positive in 18.3% (79/432) of the participants, in 9.4% (13/138) of the men and in 22.4% (66/294) of the women. ASB was identified in 14.8% (64/432) of the participants, in 5.8% (8/138) of the men and in 19.0% (56/294) of the women (P < 0.001), i.e. the probability of the second culture being positive was in men 62% and in women 85%. Including also those with lower counts (106–108 cfu/l) of Escherichia coli, according to standards for symptomatic urinary tract infection, the first culture was positive in 19.4% (84/432). The mean age of those with and without ASB was 85.8 and 84.5 years, respectively (P = 0.01).
Associations with health factors are shown in Table 3. When adjusted in a logistic regression model for the studied indicators (including age) the remaining significant factors for women were reduced mobility, urinary incontinence and oestrogen treatment (Table 4). Estimated prevalences of ASB in relation to the occurrence of reduced mobility and urinary incontinence are illustrated in Figure 1. This estimated prevalence would be 46% if these factors coincided. The same model of logistic regression applied on men left prostatic disease, history of stroke and living in a service flat as independent factors for ASB, although the small number of men with ASB made these figures uncertain.
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E. coli occurred in 68.8% (44/64) of the subjects with ASB, in 50% (4/8) of the men and in 71.4% (40/56) of the women. Klebsiella pneumoniae occurred in 9.4% (6/64), all of whom were women. Of the remaining species found, each constituted <5% of the positive cultures. E. coli were trimetoprim resistant in 14.3% and mecillinam resistant in 2.1% (one case). No E. coli resistant to nitrofurantoin, norfloxacin or cephadroxil were found.
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Discussion |
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Main findings
In this population of elderly community residents aged 80 and over, bacteriuria was found in 18.3% of the participants, in 9.4% of the men and in 22.4% of the women. ASB was identified in 5.8% of men and in 19.0% of women. Independent associated factors among women were urinary incontinence, reduced mobility and oestrogen treatment. E. coli occurred in 68.8% and were trimetoprim resistant in 14.3%.
Comments on method
This study provides information from 432 elderly residents living in the community, the participant rate was 80.4%. Since only 14% lived in service flats with a nurse stationed in the block, the results may be representative of the community elderly at large. We chose to define ASB as two consecutive positive cultures with the same species in the absence of new, obvious symptoms from the urinary tract, to minimize the risk of overestimating the prevalence of bacteriuria due to contamination. But since non-specific genitourinary symptoms are common and may vary in the elderly, it can be discussed if the concept ASB can be applied or if only bacteriuria should be used. The relatively small number of subjects in this study with a positive culture followed by a negative one, 3.5% as compared with 19% recently found in a Swedish institutional population,3 was noteworthy. This could be due to greater difficulties in obtaining an adequate urine sample from the more severely ill patients in an institution, but it might also be due to a more accurate way of sampling by our trained study nurses. Our study included also males in contrast to most other studies, but given the relatively low prevalence of ASB found, associations between ASB and health-related factors in men must be interpreted with caution. In addition, it is important to note that this was a cross-sectional study, which does not give evidence of causal relationships.
Comments on results
Most participants in this study could be characterized as quite healthy elderly community residents: only 14% lived in blocks of service flats and 74% were able to walk indoors without support or with just a stick. The prevalences of ASB in men and women in this population correspond to earlier findings among elderly persons in other non-institutional populations7,10 and are distinctly lower than the figures found in institutional populations.3,6
Impaired mobility, but not reduced functional status, reduced mental capacity or diabetes mellitus, was independently associated with ASB in women. One previous report on nursing home residents (n = 195) did not show this association11 while another report (n = 865, women) had findings in accordance with our study.12 The cause of the increased risk of bacteriuria when mobility is reduced is not clear, but impaired emptying of the bladder and increased residual volume has been discussed.6 However, a recent study did not find an association between residual urine volume and bacteriuria in the elderly in institutional care.13
The strong association between urinary incontinence and bacteriuria in women is in accordance with several other reports from more frail populations studied both in institutional care and among those living in the community.3,11,14 The bacteriuria is most probably a result of bladder dysfunction or mucosal atrophy associated with the incontinence. It can be discussed if wearing wet incontinence pads might increase the risk of acquiring bacteriuria.
The elderly with ASB seems to have an increased risk of getting recurrent symptomatic urinary tract infections6 and oestrogen is often tried to prevent these infections. This could be an explanation of the association between ASB and oestrogen treatment.
Clinical implications
An elderly woman, consulting in primary care, with urinary incontinence and with reduced mobility would have an estimated risk of almost 50% of having bacteriuria. We all have many patients fitting that description in our surgeries. If symptoms are not highly suggestive of an infection, we should avoid urine testing, since a positive test most probably will result in an unnecessary antibiotic prescription. Treatment of bacteriuria with antibiotics has not been shown to have any effect on the incontinence15 and does not reduce morbidity and mortality but leads to increased rates of bacteria with antibiotic resistance.16–18 In addition, the documented high rate of turnover of bacteriuria12 indicates difficulties in gaining lasting advantages from antibiotic treatment of ASB.
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Declaration |
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Funding: financial support for this study was provided by the county council Dalarna, Sweden and STRAMA (the Swedish Strategic Programme for the Rational Use of Antimicrobial Agents).
Ethical approval: the study was approved by the Ethics Committee of Uppsala University, Sweden.
Conflicts of interest: none.
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Notes |
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Rodhe N, Mölstad S, Englund L and Svärdsudd K. Asymptomatic bacteriuria in a population of elderly residents living in a community setting: prevalence, characteristics and associated factors. Family Practice 2006; 23: 303–307.
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References |
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1 Swedres. (2004) Swedish strategic programme for the rational use of antimicrobial agents and surveillance of resistance (STRAMA); 2005. Available at: www.strama.org.
2 Loner B, Petersson C, Cars H, Ovhed I. (2000) [Nursing home as a risky environment when it comes to antibiotic resistance. An audit study of antibiotic treatment at nursing homes in Kronoberg]. Lakartidningen 97:1251–1254.[Medline]
3 Hedin K, Petersson C, Wideback K, Kahlmeter G, Molstad S. (2002) Asymptomatic bacteriuria in a population of elderly in municipal institutional care. Scand J Prim Health Care 20:166–168.[Medline]
4 Nicolle LE. (2003) Asymptomatic bacteriuria: when to screen and when to treat. Infect Dis Clin North Am 17:367–394.[Medline]
5 Nicolle LE, Bradley S, Colgan R, Rice JC, Schaeffer A, Hooton TM. (2005) Infectious Diseases Society of America guidelines for the diagnosis and treatment of asymptomatic bacteriuria in adults. Clin Infect Dis 40:643–654.[CrossRef][ISI][Medline]
6 Nicolle LE. (1997) Asymptomatic bacteriuria in the elderly. Infect Dis Clin North Am 11:647–662.[CrossRef][ISI][Medline]
7 Boscia JA, Kobasa WD, Knight RA, Abrutyn E, Levison ME, Kaye D. (1986) Epidemiology of bacteriuria in an elderly ambulatory population. Am J Med 80:208–214.[CrossRef][ISI][Medline]
8 Statistical Yearbook of Administrative Districts of Sweden 2003. Statistics Sweden; 2003.
9 Folstein MF, Folstein SE, McHugh PR. (1975) ‘Mini-mental state’. A practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res 12:189–198.[CrossRef][ISI][Medline]
10 Nordenstam G, Sundh V, Lincoln K, Svanborg A, Eden CS. (1989) Bacteriuria in representative population samples of persons aged 72–79 years. Am J Epidemiol 130:1176–1186.
11 Eberle C, Winsemius MD, Garibaldi RA. (1993) Risk factors and consequences of bacteriuria in non-catheterized nursing home residents. J Gerontol 48:M266–M271.[Medline]
12 Abrutyn E, Mossey J, Levison M, Boscia J, Pitsakis P, Kaye D. (1991) Epidemiology of asymptomatic bacteriuria in elderly women. J Am Geriatr Soc 39:388–393.[ISI][Medline]
13 Barabas G and Molstad S. (2005) No association between elevated post-void residual volume and bacteriuria in residents of nursing homes. Scand J Prim Health Care 23:52–56.[Medline]
14 Landi F, Cesari M, Russo A, Onder G, Lattanzio F, Bernabei R. (2003) Potentially reversible risk factors and urinary incontinence in frail older people living in community. Age Ageing 32:194–199.
15 Ouslander JG, Schapira M, Schnelle JF, et al. (1995) Does eradicating bacteriuria affect the severity of chronic urinary incontinence in nursing home residents? [see comments]. Ann Intern Med 122:749–754.
16 Nicolle LE, Mayhew WJ, Bryan L. (1987) Prospective randomized comparison of therapy and no therapy for asymptomatic bacteriuria in institutionalized elderly women. Am J Med 83:27–33.[Medline]
17 Nicolle LE, Bjornson J, Harding GK, MacDonell JA. (1983) Bacteriuria in elderly institutionalized men. N Engl J Med 309:1420–1425.[Abstract]
18 Abrutyn E, Berlin J, Mossey J, Pitsakis P, Levison M, Kaye D. (1996) Does treatment of asymptomatic bacteriuria in older ambulatory women reduce subsequent symptoms of urinary tract infection? J Am Geriatr Soc 44:293–295.[Medline]
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