Streptococcus pneumoniae prevails as the most common pathogen of commu
nity-acquired pneumonia. In bacteremic disease, case fatality rates av
erage 20% and they approach 40% in older people, especially those with
underlying diseases. Pneumococcal serotypes exhibiting decreased sens
itivity to penicillin or resistance to other antibiotics complicate it
s treatment. Polysaccharide vaccine can prevent serious infection in i
mmunocompetent people.