Research report: Shifts in invasive pneumococcal disease epidemiology following the SARS-CoV-2 pandemic in Madrid, Spain: insights from a six-year hospital-based study

Invasive pneumococcal disease declined sharply during the COVID-19 pandemic and partially rebounded afterward, according to a six-year retrospective study conducted at a tertiary hospital in Madrid, Spain. Researchers identified 315 patients treated between January 2018 and December 2023, with pneumonia accounting for 76.5% of clinical presentations. The temporal pattern coincided with substantial changes in respiratory-virus circulation, although the observational study could not establish that viral activity caused the change in pneumococcal disease.

For its incidence analysis, the research team restricted calculations to 284 patients who lived within the hospital catchment area. Annualized incidence fell from 15.4 cases per 100,000 inhabitants before the pandemic, with a 95% confidence interval of 13.0–18.0, to 6.7 per 100,000 during the pandemic, with a 95% confidence interval of 5.5–8.2. In the post-pandemic period, incidence rose to 10.8 per 100,000, with a 95% confidence interval of 7.4–15.1.

The authors characterized this increase as a partial recovery because post-pandemic incidence remained below the pre-pandemic estimate. The confidence interval for the post-pandemic rate was wider than those for the earlier periods, indicating greater uncertainty in the estimated rebound. The study therefore measured a lower pandemic-period burden followed by a partial return toward the earlier level, rather than documenting a return to the original incidence.

The cohort comprised 256 adults, representing 81.3% of patients, and 59 children, representing 18.7%. Comorbidities were more prevalent among adults, affecting 78.1% of them, and adult mortality was 11.3%. Children were generally healthy but more frequently required intensive care: 67.8% of children received such care.

The researchers attributed much of this difference to empyema-related management rather than a greater underlying disease severity among children. Pneumonia was the most common clinical presentation across the study population. The investigators analyzed demographic, clinical, microbiological and virological data for the patients identified through isolation or molecular detection of Streptococcus pneumoniae from normally sterile sites.

The findings describe the population treated at one Madrid tertiary hospital and its catchment area, rather than the experience of all patients with invasive pneumococcal disease in Madrid or Spain. Only 68.6% of isolates were serotyped, and serotypes 8 and 3 predominated among those with results. The study did not test the effect of any revised vaccination strategy, so it cannot establish whether changing vaccination policy would reduce disease.

Among the serotyped isolates, serotype 11A had the highest proportion of penicillin resistance. The results nevertheless provide hospital-based information on circulating serotypes and antibiotic resistance during the study period. Respiratory viral coinfection was documented in 18.4% of cases and was more frequent in children, at 39%, than in adults.

Researchers compared temporal patterns in invasive pneumococcal disease with population-level respiratory-virus detections using a descriptive analysis. The post-pandemic rise in pneumococcal incidence coincided with substantial changes in respiratory-virus circulation, but the available data do not demonstrate a direct causal relationship between particular viruses and pneumococcal incidence. Several design limitations constrain interpretation.

Respiratory viral testing was not systematic, meaning coinfections may have been underdetected. Incomplete serotyping further restricted the available serotype-level evidence. These limitations are important because the study’s central result is temporal and observational: invasive pneumococcal disease incidence fell markedly during the pandemic and then increased again, partially recovering as respiratory-virus circulation changed.

Subject of Research: Post-pandemic changes in invasive pneumococcal disease incidence, clinical features and serotype distribution in a Madrid hospital population.

Article Title: Shifts in invasive pneumococcal disease epidemiology following the SARS-CoV-2 pandemic in Madrid, Spain: insights from a six-year hospital-based study

Article References: Brañas, P., Sanz Moreno, J. C., Castaño-Amores, M. V., Recio, R., Muñoz-Gallego, I., Villa, J., Viedma, E., & Folgueira, L. (2026). Shifts in invasive pneumococcal disease epidemiology following the SARS-CoV-2 pandemic in Madrid, Spain: insights from a six-year hospital-based study. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14688-3

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14688-3

Keywords: invasive pneumococcal disease, COVID-19 pandemic, respiratory viruses, Streptococcus pneumoniae, serotype distribution, hospital surveillance, penicillin resistance, vaccination strategy, Madrid, incidence rates, Shifts, invasive