Influence of pneumococcal serotype group on outcome in adults with bacteraemic pneumonia

The influence of infecting serotype group on outcome in bacteraemic pneumococcal pneumonia remains unclear. We performed a prospective, 10-yr observational study in an 800-bed teaching hospital. 299 adults diagnosed with pneumonia whose blood cultures showed growth of Streptococcus pneumoniae were included in the study. High invasive disease potential (H) serotypes included serotypes 1, 5 and 7F, which served as a reference category, were compared with low invasive disease potential (L) serotypes (3, 6A, 6B, 8, 19F, and 23F) and other (O) serotypes (non-H, non-L). The influence on outcome was determined for each group of serotypes after adjusting for underlying conditions and severity of illness at admission. Overall, 30-day mortality was 11%. H serotypes (n=93) infected primarily younger people and presented a higher risk of complicated parapneumonic effusion or empyema (17.2 versus 5.1%; p=0.01), with lower mortality (3.2%). The isolation of L serotypes (n=78) was an independent risk factor for 30-day mortality (OR 7.02, 95% CI 1.72-28.61), as were Charlson score (OR 1.30, 95% CI 1.08-1.58), alcohol abuse (OR 3.99, 95% CI 1.39-11.39) and severity of illness measured by American Thoracic Society (ATS)/Infectious Diseases Society of America (IDSA) criteria (OR 4.80, 95% CI 1.89-12.13). A vaccination strategy including serotypes 3, 6A, 6B, 8, 19F and 23F may improve survival in adults.