Streptococcus pneumoniae remains one of the most important causes of bacterial disease. According to statistics published by the CDC Division of Bacterial and Mycotic Diseases each year, S. pneumoniae infections cause 100,000 to 135,000 hospitalizations for pneumonia, 6 million cases of otitis media, and more than 60,000 cases of invasive disease, including 3,300 cases of meningitis. Incidence of sterile-site infections shows geographic variation from 21 to 33 cases per 100,000 population. Despite the availability of antibiotics, death occurs in 14% of hospitalized adults with invasive disease. Neurologic sequelae or learning disabilities can occur in meningitis patients. Hearing impairment can result from recurrent otitis media.

At one time, disease caused by S. pneumoniae could be reliably treated with antibiotics. However, today antibiotic resistance in S. pneumoniae is common and increasing. (For an overview of current resistance in the United States, see the recent study of resistance by the CDC journal Emerging Infectious Disease) In the United States, drug-resistant pneumococci cause at least 15,000 cases of meningitis, 7,000 cases of sepsis/bacteremia, 150,000 cases of pneumonia, and more than 1,000,000 cases of otitis media annually. Between 3-to-35% of pneumococcal illness is due to drug-resistant strains. This proportion varies widely with location and over time, but resistance has been reported throughout the world.