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Infectious Mononucleosis

Teen Version

What is mononucleosis?

Mononucleosis (mono) is a viral infection.

The symptoms of mono may include:

  • severe sore throat
  • large red tonsils covered with pus
  • swollen lymph nodes in the neck, armpits, and groin
  • fever for 7 to 14 days
  • tiredness and increased sleeping
  • enlarged spleen.

Your health care provider may do a blood test. If you have mono, your provider may be able to see unusual white blood cells in your blood.

What is the cause?

Mono is caused by the Epstein-Barr virus (EBV). This virus is transmitted in infected saliva through coughing, sneezing, and kissing. Although mononucleosis can occur at any age, it occurs more often in 15- to 25-year-olds, possibly because of more intimate contacts with others. Contrary to popular belief, mono is not very contagious. Even people in the same household rarely come down with it.

How long does it last?

Most teens have only mild symptoms for a week. Even those with severe symptoms usually feel completely well in 2 to 4 weeks.

Complications are rare and require a hospital stay when they occur. The most common problem is dehydration from not drinking enough fluids. Breathing may be blocked by large tonsils, adenoids, and other lymph tissue in the back of the throat. On rare occasions, the enlarged spleen will rupture if the abdomen is hit or strained.

How can I take care of myself?

  • Fever and medicines

    No specific medicine will cure mono. However, symptoms can usually be helped with medicines. The pain of swollen lymph nodes and fever over 102F (39C) can usually be relieved by taking acetaminophen or ibuprofen. Do not take aspirin.

    Because over 90% of people with mono will develop a severe rash if they take ampicillin or amoxicillin, these medicines should be avoided if you have mono.

  • Fluids

    To prevent dehydration, be sure you drink enough fluids. Milk shakes and cold drinks are especially good. You can also sip warm chicken broth. You are getting enough fluid if:

    • you urinate at least 3 times each day
    • your urine is not darker than usual
    • your mouth is moist and has saliva in it.
  • Sore throat treatment

    Because swollen tonsils can make some foods hard to swallow, eat soft foods as long as necessary. Sucking on hard candies can also relieve symptoms. Avoid citrus fruits. Take a daily multiple vitamin pill until your appetite returns to normal. Acetaminophen or ibuprofen can be very helpful. Do not take aspirin.

  • Activity

    You don't need to stay in bed. Bed rest will not shorten the amount of time you are sick or reduce symptoms. You can decide how much rest you need. Slow down some until you no longer have a fever.

  • Precautions for an enlarged spleen

    Your spleen may be enlarged while you have mono. A blow to the abdomen could rupture the enlarged spleen and cause bleeding. This is a surgical emergency. Therefore, all teens with mono should avoid contact sports for at least 4 weeks. If you play sports, have your provider check your spleen before you return to your sport.

    Constipation and heavy lifting should also be avoided because of the sudden pressures they can put on the spleen.

    Your provider will check you weekly until your spleen returns to a normal size.

  • Contagiousness

    Mono is most contagious while you have a fever. After the fever is gone, the virus is still carried in the saliva for up to 6 months, but in small amounts. Overall, mono is only slightly contagious. Boyfriends, girlfriends, roommates, and relatives rarely get it. If you have mono, you do not need to be isolated. However, use separate drinking glasses and utensils and avoid kissing until the fever has been gone for several days.

    The incubation period for mononucleosis is 4 to 10 weeks after contact with an infected person. This means that if a person does become infected with the virus, the symptoms will not appear until 4 to 10 weeks after the contact.

When should I call my health care provider?


  • Breathing becomes difficult or noisy.
  • Abdominal pain occurs (especially high on your left side).
  • You start feeling very sick.

Call within 24 hours if:

  • You can't drink enough fluids.
  • Signs of dehydration occur.
  • Sinus or ear pain occurs.
  • You aren't back to school by 2 weeks.
  • Any symptoms remain after 4 weeks.
  • You have other questions or concerns.
Written by B.D. Schmitt, M.D., author of "Your Child's Health," Bantam Books.
Published by McKesson Provider Technologies.
Last modified: 2006-07-31
Last reviewed: 2006-02-23
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Copyright 2006 McKesson Corporation and/or one of its subsidiaries. All Rights Reserved.
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