Strategies for the control of pneumococcal diseases

Abstract

Streptococcus pneumoniae (pneumococcus) is a Gram-positive, encapsulated bacteria that is a major cause of human disease in people of all ages. It is the most important cause of bacterial pneumonia in infancy, childhood and adult life, and the most important cause of meningitis in all age groups except children of 3 months to 2 years in whom Haemophilus influenzae type b (Hib) predominates (in the absence of Hib vaccination). Antibodies to the pneumococcal polysaccharide capsule are protective, and at present 90 capsular serotypes are recognized. The global burden of pneumococcal disease is poorly understood. It is believed to be responsible for 1-2 million deaths among children under 5 years of age every year and probably a similar number among adults. Thus, the global burden of pneumonia in adults is probably significantly underestimated at present. Strategies for the control of pneumococcal disease include control of risk factors, treatment of established cases and vaccination. In children, improved nutrition, better housing and reduced indoor air pollution are difficult to address, but should eventually reduce pneumonia rates. In adults, the risk factors are even more difficult to address, although control of alcohol and tobacco consumption and reduced transmission of HIV should all affect pneumococcal disease rates. Penicillin-resistant pneumococci are now widespread throughout the world. Where penicillin resistance occurs, penicillin should not be used to treat pneumococcal meningitis; however, penicillin, at higher doses if necessary, remains the drug of choice for the treatment of pneumococcal pneumonia, even where penicillin resistance is prevalent. There are three approaches to pneumococcal vaccination: polysaccharide vaccines (covering 23 serotypes), polysaccharide-protein conjugate vaccines (covering 9-11 serotypes) and common protein vaccines (which are not serotype-specific). Only polysaccharide vaccines are available now, but conjugate vaccines will be available soon. Polysaccharide vaccines probably have a role in protecting the elderly from pneumococcal disease, especially those at high risk. The potential role of conjugate vaccines in infants is unclear.