If I had mononucleosis 5 years ago, can I still give it to someone? I kissed this guy 4 days ago, and he is saying that I gave him mono already! Is this possible?
- Jada*

You might still be contagious, but you didn't give your guy mono. Here's why:

Like other infections, mono has an incubation period. That means it takes time for someone to start feeling ill after being infected. The incubation period for things like colds and flu is a few days. But for mono, the incubation period is 4 to 7 weeks. If you kissed a guy 4 days ago, any symptoms that he may have today are from something else, like a cold. It's just too soon for mono to show up.

So what does it mean when we say you might still be contagious, even after 5 years? The virus that causes mono is the Epstein-Barr virus (EBV for short). EBV is tricky. Experts think people with mono are most contagious for the first 18 months, but EBV stays in the body for life. The virus can show up in a person's saliva from time to time, even if it doesn't make that person feel sick with mono again. In theory, there is a very small chance that you can transmit EBV to someone else at any given point in time, even if you feel OK. Since you don't know when the virus shows up, there's not much you can do — though it can help to wash your hands regularly and avoid sharing eating or drinking utensils.

Because EBV is so sneaky, infections are common: About 95% of people have been infected with the virus by the time they are adults. Viruses like EBV are one reason why doctors are so big on hand washing. It's the best way to keep germs at bay.

Reviewed by: Elana Pearl Ben Joseph, MD
Date reviewed: February 2013

*Names have been changed to protect user privacy.