Transmission of Streptococcus pneumoniae occurs as a result of direct person-to-person contact via respiratory droplets and by autoinoculation in persons carrying the bacteria in their upper respiratory tract. The pneumococcal serotypes most often responsible for causing infection are those most frequently found in carriers.
Factors such as crowding, season, and the presence of upper respiratory infections or pneumococcal disease, such as pneumonia or otitis media, influence the spread of the organism within a family or household. Although carriage does not necessarily lead to disease, it is an important precursor for pneumococcal disease.
Pneumococcal infections are more common during the winter and in early spring when respiratory diseases are more prevalent.
The period of communicability for pneumococcal disease is unknown, but presumably transmission can occur as long as the organism appears in respiratory secretions.