Streptococcus pneumoniae: epidemiology, risk factors, and clinical features.

Streptococcus pneumoniae is the most common cause of both pneumonia overall and fatal pneumonia. Antibiotic resistance has developed worldwide and is most frequent in pneumococcal serotypes that are most prevalent in children (types/groups 6, 14, 19, and 23). The incidence of pneumococcal disease is the highest in children < 2 years of age and in adults > 65 years of age. Other important risk factors are chronic heart and lung disease, cigarette smoking, and asplenia. A 23-valent capsular polysaccharide vaccine and a heptavalent protein-polysaccharide conjugate vaccine are currently available. The latter is specially designed for pediatric use because small children respond poorly to polysaccharide antigens. Both vaccines are efficacious in prevention of invasive pneumococcal disease. The clinical presentation of pneumococcal pneumonia is variable, and neither clinical features nor laboratory or radiographic findings can reliably predict the etiology of pneumonia. Blood culture is the most important tool for establishing a definitive diagnosis, but Gram's stains and sputum culture are also of value in skilled hands. A recently developed urinary antigen test may provide a rapid diagnosis of pneumococcal pneumonia in adults. Penicillin (penicillin G/amoxicillin) remains the drug of choice for strains that are fully sensitive or have a moderately decreased susceptibility to penicillin, whereas cefotaxime and ceftriaxone are the first-line alternatives in cases with higher levels of resistance.