Abstract Rationale The polysaccaride capsular of pneumococcal serotypes, particularly those with high capsular density, could play a key role in driving systemic inflammation and severe outcomes in bacteremic pneumonia. Capsule thickness not only aids immune evasion but also actively modulates virulence, contributing to severe complications like shock and multilobar involvement. We aim to assess whether serotype capsule thickness differentially influences the association between elevated inflammation and severe complications. Methods We analyzed clinical, laboratory (including C-reactive protein levels), and microbiological data from a prospective cohort of adults with bacteremic pneumococcal community-acquired pneumonia (BP-CAP). Particular focus was placed on the capsular density of Streptococcus pneumoniae serotypes and their association with severe outcomes such as shock and multilobar involvement. Serotypes with high capsular density included 3, 6B, 11A, 18C, 19A, 19F, and 23F. Results We analyzed 938 cases of BP-CAP, of which 299 patients (31.9%) were infected by serotypes classified as having high capsular density. Overall, multilobar radiographic involvement was observed in 306 patients (32.6%), and 157 (16.7%) developed septic shock. Patients infected with high capsular density serotypes exhibited a significantly higher frequency of both multilobar involvement (39.5% compared to 29.4% in those infected with other serotypes; p = 0.002) and septic shock (23.4% vs. 13.6% in the other serotype group; p 0.05). When systemic inflammation was intense (CRP 15 mg/dl), high capsular density serotypes were substantially more frequent in patients presenting with multilobar pneumonia (43.3% vs. 17.8%; OR 1.76, 95%CI 1.22-2.54). Furthermore, the risk of septic shock was markedly increased in the high-density group associated with intense inflammation: 27.2% vs. 13.3% (OR 2.41, 95%CI 1.55-3.75). In contrast, no significant differences in multilobar involvement or shock rates were observed in patients infected with low or normal capsular density serotypes, irrespective of their CRP levels (multilobar: 23.1% vs. 30.3%, p = 0.296; shock: 16.3% vs 13.4%, p = 0.640). Conclusion1 Serotypes with high capsular density are associated with amplified systemic inflammation.2. Thick polysaccharide capsules may prolong antigenic stimulation, potentially enhancing the inflammatory response and contributing to an increased risk of shock and multilobar pulmonary involvement, suggesting a modulatory role in virulence and pathogenicity.3. Serotypes with lower capsule density do not exhibit a significant link between inflammation and severe complications, reinforcing the hypothesis that capsule thickness could be a key determinant in progression to organ dysfunction. This abstract is funded by: None
Sanz et al. (Fri,) studied this question.