Working Diagnosis:
Infectious Mononucleosis

Treatment:
Supportive treatment and rest
Remove from sport for at least 3-4 weeks from the onset of symptoms to reduce risk of splenic rupture
No evidence of quicker recovery with routine use of corticosteroids or acyclovir (corticosteroids reserved only for complications)

Editor's Comments:
1. Heterophile antibody testing has high specificity (84-100%) but can be falsely negative in 25% of patients in first week. Thus, depending on the situation and resources, a reasonable approach to diagnosis might be to start with heterophile antibody test and then get a complete blood count with a differential (either concurrently or if heterophile antibody test is negative). A lymphocyte count < 4,000 mm^3 has 99% negative predictive value while atypical lymphocytes >10% had 92.3% specificity.
Doing the specific EBV antibody tests are good confirmatory tests (97% sensitivity and 94% specificity) but take longer and are more expensive. Again, considering the timing/urgency and resources, these tests could be the secondary tests if heterophile antibody and the CBC with diff are not conclusive and suspicion is still high.

I would also advocate for doing a thorough lymph node exam, especially looking at axillary, epitrochlear and inguinal nodes (in addition to the commonly checked neck nodes).

The recent AFP article contained the statistics quoted above
Am Fam Physician. 2015 Mar 15;91(6):372-6

The utility of ultrasound is limited because size of normal spleen is so variable. In this case, getting the sono to look at other causes is reasonable if the blood tests had not come back yet to confirm mono.
Also, important to caution the infected athlete to avoid all valsalva maneuvers during the first 3-4 weeks.

For those that work with teams, it's always a good reminder that theses athletes do not need to be isolated as transmission rates are low. However, avoidance of sharing of utensils and good hand-washing is important as transmission occurs via oral secretions. Asymptomatic athletes previously infected can shed the virus.

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