Clinical factors associated with the development of Staphylococcus aureus pneumonia in patients with airway...

Staphylococcus aureus (SA) remains a major cause of infection-related mortality, and the majority of SA infections are thought to originate from strains that colonize the host prior to infection. However, clinical factors associated with the development of SA pneumonia in patients with airway SA colonization remain poorly defined. We aimed to identify clinical factors associated with the development of SA pneumonia in patients with airway SA colonization.

We conducted a retrospective observational study of 48 adult patients with airway SA colonization identified by sputum cultures at Tokyo Medical University Hospital between April 2015 and September 2022. Airway SA colonization was defined as detection of SA in two sputum cultures obtained at least one week apart, and cases of SA pneumonia developing within one year after colonization were evaluated.

Among 48 patients with SA colonization, 5 (10.4%) developed SA pneumonia. Patients who developed SA pneumonia had significantly higher stable-phase white blood cell (WBC), neutrophil, and eosinophil counts compared with those who did not. Receiver operating characteristic analysis using WBC counts to predict SA pneumonia yielded an area under the curve of 0.840 (95% confidence interval: 0.711-0.968). Although WBC counts showed discriminatory performance, their independent association with SA pneumonia could not be confirmed in this small cohort. Idiopathic pulmonary fibrosis (IPF) was significantly more frequent in patients who developed SA pneumonia and was associated with its development.

These findings suggest that progression from airway SA colonization to SA pneumonia is influenced by underlying lung disease, particularly IPF. WBC counts showed potential utility for risk stratification, although their independent predictive role remains uncertain.