My sister has mononucleosis. I drank out of her drink before we found out that she had it. Does this mean that I have mono now?
- Kyle*

Mono, or mononucleosis, is spread through direct contact with saliva. This includes sharing eating utensils, drinks, and even things like lip gloss, lipstick, or lip balm.

Because it takes about 4 to 7 weeks for symptoms to appear, a person who's infected can spread the virus without even knowing it. Though no one really knows exactly how long it takes after infection with the virus for someone to become contagious, it's pretty safe to say that a person is most contagious from right before symptoms start until they go away.

If you've shared drinks with or kissed someone who has mono, there's no way to tell whether you will get it — unless you know you've had mono before. People who have already been infected with the virus that causes mono — Epstein-Barr virus or EBV — probably won't get reinfected because they develop immunity. (Although it is possible for the virus to "reactivate," it's not because someone infects you all over again. It's because in rare cases the original virus can flare up and cause symptoms a second time).

About 95% of adults have been infected with EBV and 50% of kids are infected before age 5. So you may very well have already had mono and not known it.

If you do get the symptoms of mono — such as fever, sore throat, and tiredness — contact your doctor to find out whether you need an appointment. If so, your doctor will examine you and may also do a blood test for mono. Other viruses and some bacterial infections — such as strep — may cause similar symptoms.

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

*Names have been changed to protect user privacy.