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Normal Respiratory Flora as a Cause of Community-Acquired Pneumonia
Daniel M Musher1,2, Sirus S Jesudasen1,3, Joseph W Barwatt1,2
1Baylor College of Medicine, Houston, Texas, USA.
Background:
Intensive studies have failed to identify an etiologic agent in >50% cases of community-acquired pneumonia (CAP). Bacterial pneumonia follows aspiration of recognized bacterial pathogens (RBPs) such as Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus after they have colonize the nasopharynx. We hypothesized that aspiration of normal respiratory flora (NRF) might also cause CAP.
Methods:
We studied 120 patients hospitalized for CAP who provided a high-quality sputum specimen at, or soon after admission, using Gram stain, quantitative sputum culture, bacterial speciation by matrix-assisted laser desorption ionization time-of-flight, and viral polymerase chain reaction. Thresholds for diagnosis of bacterial infection were ≥105 colony-forming units (cfu)/mL sputum for RBPs and ≥106 cfu for NRF.
Results:
Recognized bacterial pathogens were found in 68 of 120 (56.7%) patients; 14 (20.1%) of these had a coinfecting respiratory virus. Normal respiratory flora were found in 31 (25.8%) patients; 10 (32.2%) had a coinfecting respiratory virus. Infection by ≥2 RBPs occurred in 10 cases and by NRF together with RBPs in 13 cases. Among NRF, organisms identified as Streptococcus mitis, which share many genetic features of S pneumoniae, predominated. A respiratory virus alone was found in 16 of 120 (13.3%) patients. Overall, an etiologic diagnosis was established in 95.8% of cases.
Conclusions:
Normal respiratory flora, with or without viral coinfection, appear to have caused one quarter of cases of CAP and may have played a contributory role in an additional 10.8% of cases caused by RBPs. An etiology for CAP was identified in >95% of patients who provided a high-quality sputum at, or soon after, the time of admission.
Insights
Normal respiratory flora, not just typical pathogens, can cause community-acquired pneumonia (CAP). Identifying the cause in over 95% of CAP cases is possible with early sputum analysis.
Area of Science:
- Infectious Diseases
- Microbiology
- Pulmonology
Background:
- Community-acquired pneumonia (CAP) etiology remains unidentified in over 50% of cases.
- Bacterial pneumonia is often linked to recognized bacterial pathogens (RBPs) colonizing the nasopharynx.
- This study investigated the role of normal respiratory flora (NRF) in CAP causation.
Purpose of the Study:
- To determine if normal respiratory flora (NRF) can cause community-acquired pneumonia (CAP).
- To identify the etiologic agents responsible for CAP in hospitalized patients.
- To assess the diagnostic yield of early sputum analysis in CAP cases.
Main Methods:
- Studied 120 hospitalized CAP patients with high-quality sputum specimens.
- Utilized Gram stain, quantitative sputum culture, and MALDI-TOF for bacterial identification.
- Employed polymerase chain reaction for viral detection, establishing diagnostic thresholds for RBPs and NRF.
Main Results:
- Identified recognized bacterial pathogens (RBPs) in 56.7% of patients, with viral coinfection in 20.1%.
- Found normal respiratory flora (NRF) in 25.8% of patients, with viral coinfection in 32.2%.
- Established an etiologic diagnosis in 95.8% of cases, with NRF implicated in a significant proportion.
Conclusions:
- Normal respiratory flora (NRF), with or without viral coinfection, are implicated in approximately 25% of CAP cases.
- NRF may contribute to CAP even when recognized bacterial pathogens (RBPs) are present.
- High-quality sputum analysis at admission is crucial for identifying CAP etiology in most patients.
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