The bacteria spread through the exchange of respiratory secretions during close, direct contact with an infected person.
Although "close contact" has not been clearly defined, it generally refers to individuals who have had prolonged (greater than 8 hours) contact while in close proximity (less than 3 feet) to the patient or who have been directly exposed to the patient's oral secretions during the seven days before the onset of the patient's symptoms and until 24 hours after initiation of appropriate antibiotic therapy.
Other factors that increase risk:
First-year college students living in residence halls
College students living in group settings (such as fraternities and sororities)
Those who lack a spleen or have certain immune disorders.