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Tero Kontiokari a Department of Pediatrics, University of
Oulu, Oulu, Fin-90220, Finland, b Finnish Student Health Service, Oulu,
Finland, c Laboratory of Clinical Microbiology, Oulu University Hospital,
Oulu, Fin-90220, Finland
Correspondence to: T Kontiokari tero.kontiokari{at}oulu.fi
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Abstract |
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Objective:
To determine whether recurrences of urinary tract infection can be prevented with cranberry-lingonberry juice or
with Lactobacillus GG drink.
Design:
Open, randomised controlled 12 month follow up trial.
Setting:
Health centres for university students and staff of university hospital.
Participants:
150 women with urinary tract infection
caused by Escherichia coli randomly allocated into three groups.
Interventions:
50 ml of cranberry-lingonberry juice
concentrate daily for six months or 100 ml of lactobacillus drink
five days a week for one year, or no intervention.
Main outcome measure:
First recurrence of symptomatic
urinary tract infection, defined as bacterial growth
105
colony forming units/ml in a clean voided midstream urine specimen.
Results:
The cumulative rate of first recurrence of urinary tract infection during the 12 month follow up differed significantly between the groups (P=0.048). At six months, eight (16%)
women in the cranberry group, 19 (39%) in the lactobacillus group, and
18 (36%) in the control group had had at least one recurrence. This is
a 20% reduction in absolute risk in the cranberry group compared with
the control group (95% confidence interval 3% to 36%, P=0.023,
number needed to treat=5, 95% confidence interval 3 to 34).
Conclusion:
Regular drinking of cranberry juice but
not lactobacillus seems to reduce the recurrence of urinary tract infection.
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What is already known on this topic
What this study adds
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Introduction |
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Up to 60% of women have a urinary tract infection at some point in their life.1 Sexual activity is the most important risk factor for urinary tract infection.2 At least a third of women with urinary tract infection will experience a recurrence during the following year, with recurrence being most common in the age groups 25-9 and over 55 years.3 Recurrences are a common indication for long term antimicrobial prophylaxis, but emerging antimicrobial resistance underlines the need for alternatives. 4 5
The bacteria causing urinary tract infection arise from the stools.
Dietary changes can alter the balance of faecal bacteria.6 Vaccinium berries and products containing lactobacilli have been shown
to act against the coliform bacteria that cause most urinary tract
infections.
7 8
Cranberry juice prevents bacteriuria in
elderly women,9 and locally administered lactobacilli
prevent recurrences of urinary tract infections.10 To
evaluate whether these products given orally are effective in
preventing symptomatic recurrences of urinary tract infection we
conducted an open, randomised, controlled trial.
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Participants and methods |
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Study population and design
We recruited women during 1993-7 from the Finnish student health
service at the University of Oulu and the occupational health centre
for the staff of Oulu University Hospital. Women who had a urinary
tract infection caused by Escherichia coli
(
105 colony forming units/ml in clean voided
midstream urine) and were not taking antimicrobial prophylaxis were
invited to participate. After giving informed consent, they were
randomly allocated into three groups by using tables of random numbers
and a block technique with a block size of six (fig
1).
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105 cfu/ml as the criterion for infection. If
the participant reported a urinary tract infection that was not
confirmed in our laboratory, we telephoned the diagnosing health care
facility to obtain information on any culture obtained. Only cultures
with
105 cfu/ml were accepted and recorded as
events. A urine sample with no bacterial growth was required between
two episodes before they were regarded as separate events. Women who
had three or more episodes in six months were offered antimicrobial prophylaxis.
We followed perianal and urethral colonisation with lactobacilli by
taking swab samples at the start and at three and 12 months. The
protocol was evaluated and approved by the ethics committee of the
medical faculty of the University of Oulu.
Sample size
The study end point was the first recurrence of urinary tract
infection. We calculated the sample size based on the assumption that
at least 30% of women will experience a recurrence within a
year.3 We considered a reduction in recurrences to 10% as
clinically important. To detect such a reduction with a two tailed
of 0.05 and a power of 80%, we needed 70 women in each group.
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Statistical methods
We used the Kaplan-Meier method to analyse the cumulative first
recurrence and the Breslow test to assess the differences in
occurrences at the end of the study. We calculated the incidence
density by adding the total number of episodes of urinary tract
infection and the time at risk in each group and then calculating the
rate of episodes per person year at risk. Each woman contributed days
at risk until she dropped out, became pregnant, started antimicrobial
prophylaxis, or the follow up ended. The differences in incidence of
urinary tract infection between the groups were tested assuming that
the occurrence of infection follows Poisson's distribution. We used
Cox regression analysis to control for the baseline risk factors for infection.
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Results |
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The groups were similar in their baseline characteristics with regard to the risk of urinary tract infection (table 1). The subjects had previously consumed the vaccinium berry or lactobacillus products only occasionally. Only 13 women dropped out of the study: four (8%) in the cranberry group, four (8%) in the lactobacillus group, and five (10%) in the control group, usually because of moving away. There were no major changes in nutritional status during the follow up apart from the interventions.
During the six months, eight (16%) women in the cranberry group, 19 (39%) in the lactobacillus group, and 18 (36%) in the control group had at least one episode of urinary tract infection. This is a 20% reduction in absolute risk in the cranberry group compared with the control group (95% confidence interval 3% to 36%, P=0.023, number needed to treat=5, 95% confidence interval 3 to 34). The numbers who had had a recurrence at 12 months were 12, 21, and 19 in the cranberry, lactobacillus, and control groups respectively. The cumulative first recurrence of urinary tract infection differed significantly between the groups throughout the trial (P=0.048 at 12 months; fig 2). Recurrence during the study period was significantly lower in the cranberry group than in the control group (P=0.014 at 6 months, P=0.052 at 12 months).
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We also did an analysis based on the assumption that women who dropped out of the intervention groups subsequently had a urinary tract infection whereas those who left the control group did not, but the differences in the occurrence of the first urinary tract infection remained significant (P=0.046 at 12 months). After we standardised for age, history of urinary tract infection, antimicrobial use, intercourse frequency, and fluid intake at the start of the study, the only explaining variable for the prevention of recurrences was cranberry juice (P=0.019, Cox regression analysis).
There were 98 episodes of urinary tract infection altogether during follow up, of which 21 (21%) occurred in the cranberry group, 39 (40%) in the lactobacillus group, and 38 (39%) in the control group. The difference of 0.36 in incidence densities between the cranberry and control group was significant (table 2). One woman in the cranberry group had to start antimicrobial prophylaxis, compared with five and three in the lactobacillus and control groups, respectively.
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The causative bacterium was E coli in 80% of the episodes (table 2). The proportion of episodes caused by E coli did not differ between the study groups. The number of women with perianal or urethral cultures positive for lactobacilli at any time during follow up was similar in all three groups; there were 32 (71%) in the cranberry group, 33 (67%) in the lactobacillus group, and 37 (82%) in the control group.
Fifty three women (54%) returned information about consumption of the
products. They had taken 91% of the prescribed cranberry doses and
88% of lactobacillus doses. There were no differences in the main
results of the stratified analysis between those giving this
information or not (data not shown). No adverse events were reported
except occasional complaints about the bitter taste of the cranberry juice.
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Discussion |
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Our study confirms the common belief that symptomatic recurrences of urinary tract infection can be prevented with cranberry juice. In a recent review, the previous evidence for this was found inconclusive,11 although earlier reports had suggested a beneficial effect.12 The daily consumption of 300 ml of cranberry juice reduced bacteriuria in postmenopausal women, but no beneficial effect was found among children with neurogenic bladder. 9 13 Our study population represented a typical group of women at risk of recurrences of urinary tract infection. Such women are also the most willing and able to take preventive measures. We thus believe that our result is of both medical and practical importance.
In the United States, over 11 million women each year receive antimicrobials for urinary tract infection, costing over $1.6bn (£1100m).1 Antimicrobial treatment and prophylaxis has resulted in increasing resistance to antimicrobials among uropathogenic bacteria.4 Cranberry juice provides an alternative tool for prevention of urinary tract infection that could result in decreased use of antimicrobials.
Action of cranberry juice
The berries of Vaccinium species such as cranberries and blueberries contain condensed tannins called proanthocyanidins. These can prevent the expression of the P fimbriae of E
coli.7 Proanthocyanidins are stable phenolic
compounds that are widely distributed in nature, and some of them
possess antiviral, antibacterial, antiadhesive, or antioxidant
properties.
14 15
By inhibiting bacterial cell wall
synthesis and cellular expression of adhesion molecules they inhibit
bacterial adhesion to cellular surfaces.14-16 Tannin
profiles differ between berries, and proanthocyanidin molecules of
cranberry extracts consist mainly of epicatechin.17 The
commercial product used here consisted mostly of cranberries (V
oxycoccos) but also lingonberries (V vitis-idaea),
which to our knowledge have not been analysed for proanthocyanidin concentrations.
Lactobacillus
The lactobacillus drink had no effect on urinary tract
infection, possibly because we were unable to induce lactobacilli colonisation of the periurethral area. Lactobacilli have been shown to
colonise the human intestine at doses of 108-10
cfu/day and to replace other bacterial species, especially coliform bacteria.
8 23
Consumption five times a week may have been too infrequent. Intravaginal administration of lactobacilli has been
found to reduce the number of coliform bacteria in the periurethral area and the number of urinary tract infections after antimicrobial treatment.10 In postmenopausal women, vaginal lactobacilli
are replaced by enterobacteriaceae, increasing the risk of
bacteriuria. This process can be reversed by intravaginal
administration of oestriol.24
Validity
We had to stop our trial prematurely because the manufacturer of
the cranberry juice stopped producing it. However, the difference in
the occurrence of urinary tract infection between the cranberry and
control group was clear and constant even in this limited sample size.
The compliance follow up sheet was returned by only half of the
subjects, but the reports suggested that the compliance was good and
the stratified analysis showed no differences between the subjects who
did and did not return the follow up sheet.
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Acknowledgments |
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We thank Marli and Valio for providing the study products and Eeva-Liisa Lesonen and Tuulikki Ryhänen for recruiting women to the trial at the staff health centre.
Contributors: MU initiated and coordinated the formulation of the primary study hypothesis. TK participated in the formulation of study hypothesis and design and was responsible for coordinating the collection and entry of data. KS was responsible for the recruitment of the study subjects in the Finnish student health service. MU, MN, KS, and TK discussed core ideas, designed the study protocol, and participated in the data analysis, interpretation of the results, and writing the paper. TP was responsible for the statistical analysis, participated in the interpretation of the results, and contributed to the design and writing of the paper. MK was responsible for the quality of the laboratory analysis and contributed to the design and the writing of the paper. MU and TK are guarantors of the content of the paper.
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Footnotes |
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Funding: Emil Aaltonen, Juho Vainio, and Alma and K A Snellman Foundations.
Competing interests: None declared.
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References |
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(Accepted 23 March 2001)
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