DEAR DR. DONOHUE: I am a 65-year-old woman who has been suffering from bacterial vaginosis for the past seven months. I have done everything suggested: oral antibiotics, vaginal antibiotics, creams and treatment with gentian violet. I have a terrible burning without a discharge or odor. As soon as I have sex after a treatment, it returns. I am at my wits’ end. – V.P.

ANSWER: Three common vaginal infections torment women – trichomonas (a one-celled organism), candida (a yeast) and bacterial vaginosis. The third is the most prevalent and the most difficult to treat. It tends to come back again and again.

Normally, the lactobacillus species of bacteria inhabits the vagina and keeps it on the acid side, which prevents harmful bacteria from colonizing it. If the lactobacillus bacteria decline, other bacteria – anerobes (germs that live without oxygen), another called Gardnerella and one called Atopobacterium – take over and cause trouble. They often give rise to a foul-smelling discharge and cause pain or itching.

Oral metronidazole taken for seven days or vaginal metronidazole used for five days has an 80 percent chance of curing bacterial vaginosis. For a recurrence, another course of metronidazole followed by metronidazole gel applied to the vagina twice weekly for six weeks often can stop the cycle of recurrences. Clindamycin is another effective treatment that can be used in a way similar to metronidazole to prevent relapses. A newer bacterial vaginosis medicine is tinidazole. You might not have tried that. Some investigators say that if the partner uses a condom after successful treatment, relapse is prevented. If you find that none of these effects a lasting cure, it would be worthwhile to get a second opinion since you don’t have all the classic symptoms of bacterial vaginosis. Your pain might be explained by some other condition.