# Clinical characteristics and prognostic impact of streptococcal colonization in critically ill patients with severe pneumonia

## TL;DR

This study found that Streptococcus colonization in critically ill pneumonia patients was not linked to higher mortality but was associated with shorter hospital and ICU stays.

## Contribution

The study provides new insights into the clinical impact of Streptococcus colonization in severe pneumonia patients using a large, multicenter cohort.

## Key findings

- Streptococcus colonization was not associated with increased 28-day mortality in critically ill pneumonia patients.
- Colonized patients had significantly shorter hospital and ICU lengths of stay compared to non-colonized patients.
- Streptococcus colonization was not an independent risk factor for 28-day mortality in multivariable analysis.

## Abstract

Streptococcus species are predominant ​commensal residents of the respiratory tract​ in healthy individuals and contribute to immune and metabolic regulation. However, the association between streptococcal colonization and clinical outcomes in patients with severe pneumonia remains undercharacterized. This study aimed to explore the clinical characteristics and the impact of streptococcal colonization on the prognosis of critically ill patients with pneumonia.

We conducted a multicenter, retrospective, observational cohort study of critically ill pneumonia patients admitted to 12 intensive care units (ICUs) between January 2019 and December 2023 who underwent metagenomic next-generation sequencing (mNGS). Patients were stratified into Streptococcus-colonized and non-colonized groups based on bronchoalveolar lavage fluid (BALF) mNGS results, conventional microbiological testing (CMT), and clinical assessments. Propensity score matching (PSM) was utilized to minimize baseline confounding variables. Using nearest-neighbor matching at a 1:2 ratio, baseline characteristics were balanced between groups post-matching. The primary endpoint was 28-day all-cause mortality.

A total of 1,897 patients were enrolled in this study. Among them, 21 patients under 18 years of age, 139 patients lost to follow-up within 28 days, and 4 patients with confirmed streptococcal infection were excluded. Finally, 1,733 patients met the inclusion criteria. The cohort had a mean age of 65 years, with the majority being males (1,213/1,733, 70%). Among these, 148 (8.5%) were classified as Streptococcus-colonized, and 1,585 (91.5%) were Streptococcus-colonization-negative. No significant difference in 28-day all-cause mortality was observed between the colonized and non-colonized groups (35.81% vs. 38.51%, p=0.578). Patients with Streptococcus colonization had a significantly shorter median length of stay (LOS) (17 days, interquartile range [IQR] 11–30) than those without colonization (22 days, IQR 12–33; P = 0.044). Similarly, their median intensive care unit (ICU) LOS (11 days, IQR 7–16) was also significantly shorter than that of non-colonized patients (14 days, IQR 8–25; P = 0.003). Multivariable Cox regression analysis further demonstrated that Streptococcus colonization was not an independent risk factor for 28-day mortality (HR = 1.10, 95% CI: 0.79–1.51, p=0.579).

Our findings suggest a potential role for Streptococcus colonization in improving clinical outcomes in severe pneumonia. The presence or absence of Streptococcus colonization may influence short-term prognostic benefits in critically ill pneumonia patients. Further research is needed to clarify the clinical significance and potential mechanisms of Streptococcus colonization.