Key messages

• It is not clear whether probiotics reduce the risk of developing a symptomatic urinary tract infection because the certainty of the available evidence is very low.

What is the evidence.
See evidence matrix  in Epistemonikos later

We found six systematic reviews [1],[2],[3],[4],[5],[6] that included nine primary studies [7],[8],[9],[10],[11],[12],[13],[14],[15], seven of which correspond to randomized controlled trials [7],[8],[9],[10],[11],[12],[13].

This table and the summary in general are based on the latter.

What types of patients were included*

All of the trials included women only. 

Two trials included patients with recurrent urinary tract infection [9],[11], four with an acute episode or with an episode of urinary tract infection within last year [7],[10],[12],[13] and one included healthy participants [8].

One trial included patients under 18 years [13] and the rest only included adults [7],[8],[9],[10],[11],[12].

Five trials excluded patients with use of prophylactic antibiotics [7],[9],[11],[12],[13], five excluded patients with concomitant disease [7],[9],[10],[11],[13] and three excluded pregnant women [7],[9],[11].

What types of interventions were included*

All of the trials used probiotics as intervention. 

Three trials used oral probiotics; Lactobacillus GG drink 4 x 108 CFU/100 ml 5 days a week for a year [12]; Lactobacillus GG drink 4  x 107 CFU/100 xml 5 times per month for 6 months [13]; Lactobacillus casei var rhamnosus GR-1 y Lactobacillus fermentum RC-14 1 x 109 CFU/100 ml 1 per day for 60 days [8].

The other four trials used probiotics in vaginal suppositories: Lactobacillus casei var rhamnosus GR-1  7.5 x 108 CFU by suppository twice a week for 26 weeks [9]; antibiotic treatment for 3 days with norfloxacin or cotrimoxazol, then lactobacillus casei var rhamnosus GR-1 plus Lactobacillus fermentum B-54  1.6 x 109 CFU by suppository twice a week during 2 weeks and at the end of the next 2 months [7]; Lactin-V 1 x 108 CFU by suppository 1 per day for 5 days [10]; Lactobacillus crispatus CTV-5 5x108 CFU once a day for 5 days [11].

What types of outcomes
were measured

The outcomes, as they were grouped by the systematic reviews, were the following: symptomatic urinary tract infection episodes, total adverse effects, intervention withdrawal because of adverse effects and serious adverse effects.

To whom this evidence does and does not apply

• This evidence applies to women that have presented at least one episode of urinary tract infection.
• It should be noted that one trial included patients under 18 years, so the results could be extrapolated to this population.
• Even though we did not identify studies in men, or in people with comorbidities, in absence of direct evidence it is reasonable to extrapolate the conclusions of this summary to these groups.

• The outcomes included in the summary of findings table were those considered critical for decision-making by the authors of this article. In general, they coincide with those reported by the systematic reviews.
• We did not include the outcome recurrent urinary tract infection since the analysis of this variable was not different from the result for the outcome symptomatic urinary tract infection.

• Even though it is an intervention with minimal adverse effects, it is not possible to adequately estimate the risk/benefit balance because of the uncertainty about the latter.

• Commercial formulations of probiotics, such as those evaluated in the trials, are relatively expensive. It is not possible to estimate the cost/benefit balance because of the uncertainty about the latter.

• Faced with the evidence presented in this summary, most patients and clinicians should incline against the use of probiotics to prevent urinary tract infection.
• However, there is a currently a positive opinion about probiotics between many patients and also health professionals. This could lead people who put a higher value in an uncertain benefit, or a lesser value on adverse effects or cost, to use it. It is particularly important to inform these people about the uncertainty of the existing evidence.

Differences between this summary and other sources

• The conclusions of this summary agree with most systematic reviews analysed.
• The main clinical guidelines, such as National Collaborating Centre for Chronic Conditions (NICE) [14] do not include probiotics as a therapeutic alternative for the prevention of urinary tract infections.

• The probability that future evidence modifies the conclusions of this summary is high, due to the existing uncertainty about the benefits.
• At least six ongoing trials were identified [15],[16],[17],[18],[19],[20] in the International Clinical Trials Registry Platform of the World Health Organization.
• New systematic reviews including a larger number of trials could contribute with shed more lights on this topic. We identified one ongoing systematic review [21] in PROSPERO database.