Infectious Mononucleosis is commonly known as the "kissing disease" for good reason: Epstein Barr Virus (EBV), the virus responsible for infectious mononucleosis, is usually spread via direct contact of saliva from a previously infected person with the oropharylngeal epithelium of a susceptible person. As a result, kissing is the most common way to contract mononucleosis among adolescents. Infection among infants most commonly results from eating food premasticated by an an EBV infected mother.
Outside adolescent and young adult populations, primary EBV infections rarely cause a full mononucleosis syndrome. In young children, fever and pharyngitis from primary EBV infection cannot be distinguished from other upper respitory tract infections.