Better have a backup if you use cranberry for urinary tract infections

There is an abundance of anecdotal evidence for the effectiveness of cranberry products in the treatment or prevention of urinary tract infections, but a randomized placebo-controlled trial just published in the journal Clinical Infectious Diseases indicates that there should be an alternative therapy available for backup. The authors note:

"A number of observational studies and a few small or open randomized clinical trials suggest that the American cranberry may decrease incidence of recurring urinary tract infection (UTI)."

Their double-blind, placebo-controlled trial examined the effects of cranberry on risk of recurring UTI among 319 college women who presented with an acute UTI confirmed by a positive urine culture. They were followed up until a second UTI or for 6 months, whichever came first. The data amounted to a disappointing result:

"Overall, the recurrence rate was 16.9%, and the distribution of the recurrences was similar between study groups, with the active cranberry group presenting a slightly higher recurrence rate (20.0% vs 14.0%). The presence of urinary symptoms at 3 days, 1–2 weeks, and at ≥1 month was similar between study groups, with overall no marked differences."

Although it is recognized that cranberry juice contains compounds that decrease the adherence of uropathogens—decrease the ability of bacteria to attach to urinary tract tissue—and there have been some positive reports, the authors' conclusion should be borne in mind:

"Among otherwise healthy college women with an acute UTI, those drinking 8 oz of 27% cranberry juice twice daily did not experience a decrease in the 6-month incidence of a second UTI, compared with those drinking a placebo."

A paper published years ago in the The Journal of Urology sheds light on why we have a negative trial like this that contradicts other studies and anecdotal reports. The authors investigated the properties of d-mannose, another 'natural' agent used to treat urinary tract infections by reducing bacterial adherence:

"The effect of D-mannose on adherence of 73 Escherichia coli strains to vaginal and buccal epithelial cells from women with recurrent urinary tract infections...was tested. Urinary, vaginal or anal isolates from women with such infections were used."

They found that there was a significant difference depending on the strain of bacteria:

"Of the strains 66 (90 per cent) demonstrated adherence to epithelial cells. D-mannose inhibited completely the adherence of 25 strains (42 per cent) that adhered to vaginal cells and inhibited an additional 11 strains (18 per cent) by at least 50 per cent. Similar results were obtained with buccal cells."

This highlights the obvious clinical fact: when treating an infection, the effectiveness of any kind of antimicrobial intervention will vary according to the strain (not just the species) of the pathogen. Sensitivity should be determined beforehand whenever possible; otherwise have a backup.