Since mono is spread from person to person, avoiding close personal contact with infected individuals and practicing excellent hygienic practices can help prevent transmission of the virus. This includes avoiding sharing contaminated utensils like toothbrushes and drinking glasses. However, since periodic reactivations of the virus infection seem to occur in healthy individuals and because many infected people who may transmit the virus to others will not have symptoms of the condition, prevention is extremely difficult. In fact, these individuals without symptoms are believed to be the primary source of transmission of the virus. The fact that up to 95% of adults have antibodies to EBV suggests that prevention of the infection is difficult if not impossible. It is not known why some people develop the symptoms of mono while others appear to acquire the EBV infection without having symptoms. It is possible that many infections occur and produce mild symptoms and are not recognized as mono, while other infections may not produce symptoms at all.
If the patient has more than 20 percent atypical lymphocytes or more than 50 percent lymphocytes with at least 10 percent atypical lymphocytes, infectious mononucleosis is quite likely, and further confirmation of the diagnosis is not needed. A positive result of a heterophile antibody test also is strong evidence in favor of a diagnosis of infectious mononucleosis. A negative result of an antibody test, particularly during the first week of illness, may indicate that the patient does not have infectious mononucleosis. However, it also could be a false-negative result or could indicate that the patient has an infectious mononucleosis–like syndrome caused by CMV or toxo-plasmosis. The patient should be treated symptomatically, and if the patient does not clinically improve within five to seven days, a second heterophile antibody test should be performed. If an accurate diagnosis is urgently required (for example, in a competitive athlete who wants to return to competition as soon as possible), a VCA-IgM test may be selected. A negative result is strong evidence against the diagnosis of infectious mononucleosis.