Clinical Report: Streptococcus anginosus Group as a Cause of Community-Acquired Pneumonia
Overview
Streptococcus anginosus group (SAG) bacteria, traditionally considered oral commensals, are increasingly recognized as causative agents of empyema secondary to community-acquired pneumonia (CAP). This retrospective study identified SAG, particularly Streptococcus intermedius, as a frequent pathogen in empyema cases, often misdiagnosed due to subacute pneumonia presenting as atelectasis on imaging.
Background
Community-acquired pneumonia is a major cause of morbidity and mortality worldwide, yet its etiologic diagnosis remains elusive in many cases. Thoracic empyema, a complication of pneumonia, often reveals the causative organisms, commonly including Streptococcus pneumoniae and Staphylococcus aureus. The Streptococcus anginosus group, part of normal oral flora, has been increasingly isolated in empyema but not traditionally linked to CAP. Identifying SAG in pure culture from empyema fluid suggests its direct role in pneumonia pathogenesis.
Data Highlights
Parameter
Findings
Number of patients with SAG empyema
37
Pure SAG cultures
23 patients
Polymicrobial SAG cultures (pSAG)
14 patients
Most common species isolated
Streptococcus intermedius
CT scans with Hounsfield unit measurements
13 patients
Predisposing factors
Substance use (alcohol, sedatives, narcotics), cancer, esophageal surgery with mediastinitis
Key Findings
SAG bacteria, especially S. intermedius, are significant pathogens in empyema secondary to CAP.
Empyema cases with pure SAG cultures indicate SAG as the primary pneumonia pathogen rather than contaminant flora.
Subacute pneumonias caused by SAG are often misdiagnosed as atelectasis on initial CT imaging.
Measurement of Hounsfield units on contrast-enhanced CT scans helps differentiate pneumonia from atelectasis adjacent to empyema.
Patients with polymicrobial SAG empyema frequently have cancer or prior esophageal surgery leading to mediastinitis.
Substance use is a common predisposing factor in patients with SAG empyema.
Clinical Implications
Clinicians should consider SAG bacteria as potential causative agents in cases of community-acquired pneumonia complicated by empyema, especially when imaging suggests adjacent atelectasis. Utilizing contrast-enhanced CT with Hounsfield unit measurements can aid in accurate diagnosis. Awareness of predisposing factors such as substance use and malignancy-related mediastinitis can guide clinical suspicion and management.
Conclusion
The Streptococcus anginosus group, particularly S. intermedius, is an underrecognized cause of community-acquired pneumonia leading to empyema. Improved diagnostic approaches, including imaging analysis and culture interpretation, are essential for appropriate identification and treatment.
References
Author/Source/Year -- The Role of Streptococcus anginosus Group in Community-Acquired Pneumonia: An Overlooked Pathogen
Large Swedish cohort study finds children hospitalized for respiratory syncytial virus at older ages have greater risk of subsequent bacterial pneumonia
