Question:

Is mononucleosis contagious? My 19-year-old daughter has been diagnosed with mono. Should she stay away from her 86-year-old grandparents when they visit?

Answer:

Mononucleosis ("mono") is an illness caused by a new infection with a virus, most often the Epstein-Barr virus, which is very contagious. Practically every adult is infected with it.

However, only a minority of people get mono when they are first infected with the virus. Many people just get a brief "cold." Some people don't get sick at all. Whether people get sick when they first catch the Epstein-Barr virus or not, the virus remains alive in their bodies for the rest of their lives. Most of the time, it is "asleep." It just sits inside some of your blood cells or throat cells. It does not reproduce and or cause any illness.

In the United States, most people become infected with the Epstein-Barr virus by the time they are 20. So the chances are better than 90% that your daughter's grandparents already are infected with the virus. It is probably asleep within them. If they are already infected, being exposed again poses no risk to them.

Also, it isn't easy to pass the Epstein-Barr virus from one person to another. The best known way to pass the virus is by being exposed to an infected person's saliva. That's why mono is sometimes called "the kissing disease."

People with mono are advised not to kiss other people while they are sick and for a few weeks after they are recovered. If a person with mono is coughing, I tell them to cough into a tissue or handkerchief, although it is not proved that the Epstein-Barr virus can be transmitted by coughing.

So, there is little or no risk to your grandparents from your daughter's mono, and no need to quarantine your daughter. She should just avoid kissing people until a few weeks after she has recovered.