Tips & Training

Mononucleosis: Guidelines for Safe Return to Training and Competition

by James N. Johnson, MD
USA Swimming National Team Physician
Stanford University Team Physician

Mononucleosis is an infectious illness caused by the Epstein-Barr Virus which commonly affects swimmers during periods of peak training.  The prime risk of continued training with mononucleosis is splenic rupture.  This risk is highest in the first three weeks of illness, but has been reported up to seven weeks after the onset of symptoms.  A secondary risk in athletes in training-oriented sports like swimming is developing a chronic fatigue state or even more significant neurological complications.  To avoid these potential serious risks, coaches, parents, and athletes need to be alert for the symptoms of mononucleosis (mono) and have a safe plan for return to activity.

Mono commonly presents during peak training periods of the fall and winter months when the athletes are very fatigued and are also immersed in many other activities including final exams and holiday social and family activities.  Fatigue is a common complaint; so, mono can be difficult to recognize.  The most common early sign is a sore throat. A second sore throat and increasing fatigue developing within two weeks of the first is a red flag for mono.  This time period also coincides with the highest risk for splenic rupture; so evaluation and examination by a physician is of paramount importance.  Though contact sports carry the highest risk of this complication, there are case reports of rupture in non-contact athletes.  Often a coach will also notice decreased practice and competition performance atypical for the affected athlete.  This should be a second red flag to encourage evaluation by a physician.  Multiple teammates with similar symptoms can also be mistaken for training-related fatigue, but can be a presentation of multiple simultaneous case of mono which is not uncommon.  Mono is highly contagious with an incubation period of 30-50 days from exposure until expression of disease and a six-month period of viral shedding after exposure.  Accordingly, once one case is diagnosed, heightened awareness of potential subsequent cases should follow.

Athletes will all express the disease differently; so, diagnosis and treatment needs to be symptom-driven. In other words, the whole team doesn’t need to be tested for mono if one member is diagnosed.  Close contacts are at increased risk but many often do not express the illness.  Once an athlete is ill and then tests positive for mono, rest and treatment of symptoms should follow.  Rest is crucial in the first four weeks following diagnosis.  The lymphocyte count and liver function test take 21-28 days to normalize and the spleen is at its greatest risk of rupture during this period.  Often with swimmers, one week out of school and out of all training is required and then some light swimming  and return to classes in a graduated fashion can follow over the next three weeks.  A protocol that has been successful in preventing recurrence and continued fatigue involves gradual increase over a three week period allowing no more than 30 minutes of light swimming daily at a a low-level intensity (some data suggests that low level activity for this period of time may boost immunity).  The problem with increasing faster is starting the athlete on a roller-coaster of feeling good one day and subsequently doing more than they should causing them to have increased symptoms on the following day.  Every athlete will have a slightly different presentation of mono.  Some will be able to return slightly sooner and others will take up to two-three months to return to full activity, which underscores the importance of close follow-up with a physician.

Finally, to prevent spread of disease, common sense is the best practice.  Counsel athletes to not share water bottles, towels, or swim suits; and to wash all of these items regularly. In addition, athletes should get 8-9 hours of sleep nightly, eat well, and avoid alcohol and tobacco use.  Swimmers are in a demanding sport which requires extra vigilance to avoid fatigue-related illness, of which mono is the most common.  If athletes, coaches, and parents have an increased awareness of the symptoms of mono, know some strategies for a safe return, and avoid the factors which can prolong or spread the disease,  healthy and fast swimming can be the end result.


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