I understand your concern.
Urine and blood culture
may not yield anything until there is urinary tract infection
or blood stream infection and the tests results came was as expected. Yeast in the vagina is a normal flora how ever if it is responsible for symptoms in her and all other causes of such symptoms are excluded, your wife may need a treatment for yeast, if she is having it currently.
Visit a dermatologist
or venerologist or a gynecologist. You may find it helpful.
Hope it is clear.