Streptococcus pneumoniae (pneumococcus) is a gram-positive bacterium belonging to streptococci. Pneumococcal disease, caused by this bacterium, is one of the most common causes of childhood morbidity and mortality in the world. Pneumococcus is able to infect most body tissues. It is responsible for noninvasive infections of the upper respiratory tract mucosa: sinusitis, otitis media, pneumonia, and serious invasive diseases such as meningitis or sepsis.
Pneumococcal colonization is most common in children under 5 (35-60%) and decreases with age. It is estimated that 29-35% of primary school children and 9-25% of adolescents and adults are carriers of Streptococcus pneumoniae. Carrier frequency is higher in places occupied by larger groups of people (nurseries, kindergartens, prisons, nursing homes), as pneumococcus is transmitted by direct contact and by droplet route.