As Streptococcus pneumoniae was considered the etiological agent of nearly all the cases of pneumonia at the beginning of the 20th century, and today is identified in fewer than 10–15% of cases, we analyze the possible causes of such a decline.
Extensive use of early empiric antimicrobial therapy, discovery of previously unrecognized pathogens, availability to newer diagnostic methods for the recognition of the pneumonia pathogens (PCR, urinary antigens, monoclonal antibodies etc.) and of improved preventive measures, including vaccines, are some of possible explanations of the declining role of S. pneumoniae in the cause of pneumonia.
The 14-valent and the 23-valent capsular polysaccharide pneumococcal vaccines were licensed in 1977 and 1983, respectively. The seven-valent protein-conjugated capsular polysaccharide vaccine, approved for routine use in children starting at 2 months of age, was highly effective in preventing invasive pneumococcal disease in children but also in adults because of the herd effect. In 2010, the 13-valent protein-conjugated capsular polysaccharide vaccine replaced seven-valent protein-conjugated capsular polysaccharide vaccine. With the use of conjugated vaccines, a decrease of the vaccine-type invasive pneumococcal disease for all age groups was observed. Both the direct effect of the vaccine and the so-called herd immunity are considered responsible for much of the decline.
Pulmonary Diseases Division, Department of Medicine, Hospital de Clínicas, Universidad de Buenos Aires, Buenos Aires, Argentina
Correspondence to Carlos M. Luna, MD, Pulmonary Diseases Division, Department of Medicine, Hospital de Clínicas, Universidad de Buenos Aires, Arenales 2557, piso 1, dto A, Ciudad Autónoma de Buenos Aires, Capital Federal, CP 1425 Buenos Aires, Argentina. Tel: +54 9 11 5756 1535; fax: +54 11 5950 8929; e-mail: firstname.lastname@example.org