Cranberry juice capsules and urinary tract infection post-surgery: Results of a randomized trial 

In a randomized trial from 2015, 160 patients undergoing elective gynecologic surgery were randomized to receive 720 mg cranberry fruit extract or placebo twice daily for six weeks post-op. The occurrence of UTI was significantly lower in the cranberry group, 19%, compared to 38% in the placebo group. 

References:

Foxman B, Cronenwett AEW, Spino C, et al. (2015). Cranberry juice capsules and urinary tract infection post surgery: Results of a randomized trial. Am J Obstet Gynecol. 213(2): 194.e1-8