Changing Epidemiology of Severe Pneumococcal Pneumonia in Adults at Tertiary Hospital between 2010-2024.

BACKGROUND: The epidemiology of pneumococcal pneumonia can be influenced by vaccine implementation, serotype replacement, and viral circulation. We aimed to investigate 15-year trends in the epidemiological and clinical characteristics of severe pneumococcal pneumonia patients requiring intensive care unit (ICU) admission. METHODS: We analyzed data from a prospective cohort of adult patients with severe pneumonia admitted to the 28-bed medical ICU of a 2,700-bed tertiary hospital in South Korea between 2010 and 2024. Temporal changes in incidence, resistance to antimicrobial agents, frequency of co-infections, and mortality were evaluated across three 5-year periods. RESULTS: Among 2,511 ICU patients with severe pneumonia, 140 (5.6%) had pneumococcal infections. The proportion of pneumococcal cases decreased from 9.9% in 2010-2014 to 4.2% in 2015-2019, and further to 2.2% in 2020-2024 (p<0.001 for trend). Conversely, ceftriaxone non-susceptibility rates rose sharply from 4.8% to 16.7% and 45.5% across the same periods (p<0.001). Co-infections were frequent and increased significantly, largely due to respiratory viruses, with rates of 48.9%, 61.8%, and 77.8%, respectively (p=0.02). Influenza was the predominant co-pathogen during 2015-2019, whereas SARS-CoV-2 was most frequent in 2020-2024. The 90-day mortality rates remained stable over time (29.5%, 38.2%, and 27.8%, p=0.64). CONCLUSIONS: In this single-center ICU cohort, the proportion of severe pneumococcal pneumonia cases decreased over the 15-year period, whereas ceftriaxone non-susceptibility and viral co-infections became more frequent. These trends should be interpreted cautiously given the lack of serotype and individual vaccination data and incomplete susceptibility results. Continued surveillance of pneumococcal disease, antimicrobial resistance, and respiratory co-infections is warranted.