Abstract: We included nine studies that involved 735 people in this review. Four studies compared probiotic with placebo, two compared probiotic with no treatment, two compared probiotics with antibiotics in patients with UTI, and one study compared probiotic with placebo in healthy women. All studies aimed to measure differences in rates of recurrent UTI. Our risk of bias assessment found that most studies had small sample sizes and reported insufficient methodological detail to enable robust assessment. Overall, there was a high risk of bias in the included studies which lead to inability to draw firm conclusions and suggesting that any reported treatment effects may be misleading or represent overestimates. We found no significant reduction in the risk of recurrent symptomatic bacterial UTI between patients treated with probiotics and placebo (6 studies, 352 participants: RR 0.82, 95% CI 0.60 to 1.12; I2 = 23%) with wide confidence intervals, and statistical heterogeneity was low. No significant reduction in the risk of recurrent symptomatic bacterial UTI was found between probiotic and antibiotic treated patients (1 study, 223 participants: RR 1.12, 95% CI 0.95 to 1.33). The most commonly reported adverse effects were diarrhoea, nausea, vomiting, constipation and vaginal symptoms. None of the included studies reported numbers of participants with at least one asymptomatic bacterial UTI, all-cause mortality or those with at least one confirmed case of bacteraemia or fungaemia. Two studies reported study withdrawal due to adverse events and the number of participants who experienced at least one adverse event. One study reported withdrawal occurred in six probiotic participants (5.2%), 15 antibiotic participants (12.2%), while the second study noted one placebo group participant discontinued treatment due to an adverse event. No significant benefit was demonstrated for probiotics compared with placebo or no treatment, but a benefit cannot be ruled out as the data were few, and derived from small studies with poor methodological reporting. There was limited information on harm and mortality with probiotics and no evidence on the impact of probiotics on serious adverse events. Current evidence cannot rule out a reduction or increase in recurrent UTI in women with recurrent UTI who use prophylactic probiotics. There was insufficient evidence from one RCT to comment on the effect of probiotics versus antibiotics.

Plain-language summary: We conducted a literature search up to September 2015 and nine studies were eligible for inclusion according to our selection criteria. The nine studies reported data on 735 participants and investigated probiotics for preventing UTI: seven studies involved women or girls with recurrent UTIs, one looked at children with abnormal urinary tracts, and one investigated UTI in healthy women. Generally, studies were poor quality with high risk of bias. Aside from the different populations, there were also many different species of probiotics used, different dosage forms such as vaginal and oral, and probiotics were given for varying lengths of time. All of these factors may have affected our results. Most studies did not collect information on adverse effects so we were unable to estimate any harms associated with probiotic therapies. We found no significant reduction in the risk of recurrent symptomatic bacterial UTI between patients treated with probiotics and placebo and no significant reduction in the risk of recurrent symptomatic bacterial UTI was found between probiotic and patients treated with antibiotics. The currently available evidence shows no reduction in UTI using probiotics.