Serotype prevalence in adults hospitalised with pneumococcal non-invasive community-acquired pneumonia

Background The distribution of pneumococcal serotypes implicated in non-invasive community-acquired pneumonia (CAP) in adults is currently unknown. Methods A prospective observational cohort study was conducted over 2 years in a large UK teaching hospital trust. Urine samples, in addition to routine blood and sputum samples, were obtained from consecutive adults admitted to the hospital with CAP. Pneumococcal serotype was determined from urine samples using a validated multiplex immunoassay which detects 14 serotypes. Results Of 920 patients with CAP, 366 had pneumococcal CAP; 242 had a serotype determined. Thirty-day mortality was 10% for all-cause CAP and 9.6% for pneumococcal CAP. Annual incidence of pneumococcal CAP was 36.5 per 100 000, increasing from 12.1 to 274.1 per 100 000 for ages 16-44 years and >= 85 years, respectively. The most prevalent serotypes were 14, 1, 8, 3 and 19A. Less invasive serotypes were significantly associated with increasing age (OR per increasing age group: 1.5, 95% CI 1.2 to 1.9, p<0.001) and co-morbidity (OR per increasing Charlson index group: 1.4, 95% CI 1.0 to 2.0, p=0.036), and with higher 30-day mortality (OR adjusted for age and comorbidity: 5.5, 95% CI 1.2 to 25.3, p=0.028) compared with highly invasive serotypes. The proportion of patients in whom serotypes contained within the seven-valent childhood pneumococcal conjugate vaccine was identified increased with age (15.6% for patients aged 16-44 years, 41.0% for patients aged >= 85 years; p<0.05). Conclusions In adult invasive and non-invasive pneumococcal CAP, the most common serotypes implicated were 14, 1, 8, 3 and 19A. Age and comorbidity were associated with the distribution of serotypes identified.