I don't know if roselle can be used like cranberry.
Norita sent me her favorite photo of Hibiscus sabdariffa.
"Here in Panama it is called saril. It's mostly used as a refreshing drink at Christmas time which is when it is available. Urologists in Panama are recommending cranberry juice, which is imported and expensive, about $8 a gallon, supposedly it prevents urinary type infections. Here at home we all drink it. I just wonder if saril isn't just as effective and quite a bit more reasonable."
Hmm. Let's see what medline has to say:
Ali BH, Al Wabel N, Blunden G.: Phytochemical, pharmacological and toxicological aspects of Hibiscus sabdariffa L.: a review. Phytother Res. 2005 May;19(5):369-75.
In the abstract, the authors state that the roselle, red sorrel, karkade (there's many many more names for this particular plant) contains vitamin C, mainly.
A quote: "In healthy men, consumption of H. sabdariffa has resulted in significant decreases in the urinary concentrations of creatinine, uric acid, citrate, tartrate, calcium, sodium, potassium and phosphate, but not oxalate."
Another: "In rats and rabbits, the extract showed antihypercholesterolaemic, antinociceptive and antipyretic, but not antiinflammatory activities."
Cranberry works because it stops bacteria from adhering to the bladder wall. I don't know if roselle contains the same "A-Type proanthocyanidin trimers from cranberry that inhibit adherence of uropathogenic P-fimbriated Escherichia coli".
So if you try roselle to prevent urinary tract infections let us know how it turns out. Thanks!