Five decades of pneumococcal meningitis in Spain: a single-centre, clinical and genomic, retrospective, observational study

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BACKGROUND: Pneumococcal meningitis remains a major threat, with high fatality rates and long-term sequelae, despite advances in vaccination and treatment. We aimed to examine the associations between pneumococcal serotypes, Global Pneumococcal Sequence Cluster (GPSC), antimicrobial resistance, source of infection, and clinical outcomes in adults with pneumococcal meningitis. METHODS: In this single-centre, clinical and genomic, retrospective, observational study, we analysed all laboratory-confirmed cases of adult pneumococcal meningitis recorded at Hospital Universitari de Bellvitge, Spain. Clinical data were obtained from a prospectively maintained clinical database and linked to microbiological and genomic data by unique patient identifiers. Clinical sources of infection were classified as cerebrospinal fluid leakage, acute otitis media, or haematogenous origin. Disease severity was defined as shock at presentation, sequelae as any persistent neurological deficit at discharge, and mortality as death within 30 days. Serotype data were available for 265 isolates, and whole-genome sequencing was done on 200 viable isolates. For outcome analyses, patients who did not receive dexamethasone were excluded. Serotype, GPSCs, antimicrobial susceptibility, phylogenetic, and genome-wide association study (GWAS) data were analysed to assess determinants of meningitis source, disease severity, sequelae, and 30-day mortality. FINDINGS: 387 adult patients (median age 58 years [IQR 45-68]; 54% male) with pneumococcal meningitis were recorded between Jan 1, 1974, and Dec 31, 2023. Acute otitis media was the most frequent source of pneumococcal meningitis (174 [45%] of 387 cases) and was mainly caused by serotype 3 (pneumococcal conjugate vaccine [PCV]13; GPSC12). The 30-day case-fatality rate in this group was 17 (10%) of 174 (95% CI 5·8-15·2). Haematogenous episodes accounted for 104 (27%) of 387 cases and had a significantly higher 30-day case-fatality rate (50 [48%] of 104; 95% CI 38·2-58·1; p<0·0001) with a higher frequency of serotype 4. Cerebrospinal fluid leakage accounted for 105 (27%) of 387 cases and had the lowest 30-day case-fatality rate (nine [9%] of 105; 95% CI 4·0-15·6) and broader serotype diversity. The introduction of PCV7 and PCV13 resulted in declines in vaccine-targeted serotypes and β-lactam resistance. Whole-genome sequencing identified 60 distinct GPSCs. Among prevalent lineages, GPSC16 (20 [10%] of 200; serotypes 19A and 23F) and GPSC6 (18 [9%] of 200; serotypes 9V, 11A, and 14) were associated with β-lactam resistance. GWAS did not identify genetic variants significantly associated with severity, sequelae, or mortality. INTERPRETATION: This longitudinal study provides a comprehensive view of adult pneumococcal meningitis over five decades, revealing changes in sources of infection, serotype distribution, pneumococcal lineages, and antimicrobial resistance patterns over time. Lineage-level findings suggested variability in clinical outcomes, underscoring the importance of continued genomic surveillance and supporting consideration of broader vaccine targets. GPSC12 predominance and its association with mortality and more severe outcomes highlight the need for preventive measures against serotype 3, although these findings require confirmation in larger multicentre cohorts. FUNDING: Instituto de Salud Carlos III, cofunded by European Social Fund, and the Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, and the Centro de Investigación Biomédica en Red de Enfermedades Infecciosas, both at the Instituto de Salud Carlos III.

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