This prospective single-center cohort assessed adults with severe pneumonia admitted to the 28-bed medical ICU of a 2,700-bed tertiary hospital in South Korea between 2010 and 2024. Among 2,511 ICU patients with severe pneumonia, 140 (5.6%) had infections attributed to Streptococcus pneumoniae (pneumococcal pneumonia). The study evaluated temporal changes in incidence, antimicrobial resistance, frequency of co-infections, and mortality across three consecutive 5-year intervals within the 15-year span.
Patients were drawn from a prospective ICU severe pneumonia cohort at a high-volume tertiary referral center. Temporal comparisons divided the study interval into three periods: 2010–2014, 2015–2019, and 2020–2024. The analysis focused on (1) the proportion of severe pneumonia attributable to pneumococcus, (2) rates of antimicrobial non-susceptibility (reported notably for ceftriaxone), (3) the frequency and identity of co-infecting pathogens, particularly respiratory viruses, and (4) 90-day mortality. The authors report that some susceptibility data were incomplete and that serotype and individual vaccination information were not available.
Over the 15-year observation window, the proportion of ICU severe pneumonia cases caused by pneumococcus declined significantly. Reported proportions were 9.9% in 2010–2014, 4.2% in 2015–2019, and 2.2% in 2020–2024 (p<0.001 for trend). The absolute number of pneumococcal cases across the full cohort was 140 of 2,511 severe pneumonia admissions. The authors note that vaccine implementation, serotype replacement, and viral circulation are known drivers of pneumococcal epidemiology, but specific serotype and vaccination data were not reported here.
While the proportion of pneumococcal cases fell, resistance to key antimicrobials increased. Ceftriaxone non-susceptibility rose sharply across the three periods: 4.8% in 2010–2014, 16.7% in 2015–2019, and 45.5% in 2020–2024 (p<0.001). These results indicate a marked escalation in reduced susceptibility to a commonly used third‑generation cephalosporin among ICU pneumococcal isolates in this cohort. The authors caution that some susceptibility results were incomplete, which limits interpretation.
Co-infections were common among patients with severe pneumococcal pneumonia and increased significantly over the study periods. Overall co-infection rates were 48.9%, 61.8%, and 77.8% for 2010–2014, 2015–2019, and 2020–2024, respectively (p=0.02). The rising frequency was largely driven by respiratory viruses. Influenza was the predominant viral co-pathogen in 2015–2019, whereas SARS‑CoV‑2 was the most frequent co-pathogen in 2020–2024, reflecting pandemic-era viral circulation patterns impacting ICU pneumococcal cases.
Ninety-day mortality among ICU patients with pneumococcal pneumonia did not show a statistically significant change across the three periods. The reported 90-day mortality rates were 29.5% (2010–2014), 38.2% (2015–2019), and 27.8% (2020–2024) (p=0.64). Despite shifts in case proportion, antimicrobial resistance, and co-infection patterns, overall longer-term mortality remained relatively stable in this cohort.
The authors highlight several limitations that affect interpretation. Serotype-specific data for Streptococcus pneumoniae were not reported, and individual vaccination status was not available, both of which are important for understanding vaccine impact and serotype replacement. Additionally, some antimicrobial susceptibility results were incomplete. The study is single-center and involves ICU patients only, which may limit generalizability to other settings or to non‑critically ill populations.
In this tertiary ICU cohort over 15 years, the proportion of severe pneumococcal pneumonia decreased while ceftriaxone non-susceptibility and the proportion of cases with respiratory viral co-infections increased. These diverging trends suggest evolving clinical challenges: decreasing case burden but greater antimicrobial resistance and more frequent viral co-pathogens among the remaining severe cases. The authors conclude that continued surveillance of pneumococcal disease, antimicrobial resistance patterns, and respiratory co-infections is warranted. Given the absence of serotype and vaccination data and incomplete susceptibility testing, the observed trends should be interpreted cautiously and prompt further investigation with more complete microbiological and immunization information.