DEAR DR. DONOHUE: One year after I had been dating my girlfriend, she was diagnosed with genital warts. She assures me she has not been with anyone else. Her doctor said that, although it is highly unlikely, the warts could come from the same virus that causes warts on her hand. My doctor says the only way to contract these warts is through sexual activity. I could use your advice. – F.S.

ANSWER: Take comfort in a truism. Medical knowledge is subject to change. Things said confidently are not always known confidently. That applies to the papillomaviruses, the viruses of warts, and to their transmission.

There are more than 80 different kinds of papillomavirus, and each has its own idiosyncrasies. Some infect only the external skin; others, the genital area; and a few can infect both sites. In a study done in England, transmission from a nongenital site to the genital region was reported.

Admittedly, genital warts are most often sexually spread. But according to the information that comes from England, nonsexual transmission, although rare, is probably possible.

The second factor has to do with genital warts’ incubation period — the time from first contact with the skin to the appearance of a wart. The usual incubation period is three months. However, in some instances the incubation period is measured in years. A long incubation, therefore, could be a reasonable explanation for your girlfriend’s warts.

It is not stretching matters to accept your girlfriend’s protestation as being true.

Genital warts and herpes infections create problems in relationships because there are many misconceptions about the two. The newly printed pamphlet on those topics can dispel erroneous beliefs and bring people up-to-date on all aspects of these common infections. Readers can obtain a copy by writing: Dr. Donohue — No. 1202, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.50 U.S./$6 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: What can be done for a mouth with a persistent salty taste? I don’t salt my food. I never put a salt shaker on the table. I am fastidious about brushing my teeth after eating. What is going on? – M.R.

ANSWER: The first person to consult about a salty taste in the mouth is your dentist, who will look for tooth decay, infected gums or dentures that fit poorly and ooze adherent into the mouth.

The second place to look is your medicines. It is best to do this in the presence of your doctor so no medication is forgotten.

Rare conditions that can lead to a salty taste include vitamin B-12 deficiency or an underactive thyroid gland.

If the search proves unrewarding, then chew sugarless gum or let sugarless hard candy dissolve in your mouth to stimulate saliva production. A brisk flow of saliva can often wash away the salty taste.

DEAR DR. DONOHUE: How often does a person who takes Coumadin have to have a blood test? I have been taking it for five years for heart fibrillation. My old doctor had me get a blood test once a month. He has retired. My new doctor insists I have the test every two weeks. Who is right? – R.J.

ANSWER: Coumadin is a blood thinner. In people with atrial fibrillation, their upper heart chambers — the atria — do not contract to empty blood into the lower ventricles, the pumping chambers. The atria quiver. Quivering atria are a setup for formation of blood clots.

A blood clot in the atria can spell catastrophe. Pieces of the clot can break loose from the main clot and be swept by the circulation into brain blood vessels. There they can block those vessels, with the result being a stroke. That is the reason why people with atrial fibrillation take blood-thinning medicines.

When a person first starts taking Coumadin, doctors want blood tests done every two weeks to see if the patient is taking too little or too much Coumadin. When the tests consistently indicate that the blood is safely thinned, then the tests can be spaced out to one a month.

Your new doctor might have a reason for getting more frequent tests — one that you and I don’t know.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475.