Exploring the microbial landscape: uncovering the pathogens associated with community-acquired pneumonia in hospitalized patients

Abstract

Objectives: This study aimed to investigate the etiology, clinical features, and outcomes of community-acquired pneumonia (CAP) in adults. Understanding the causative pathogens is essential for effective treatment and prevention.

Design: Between 2016-2018, 518 hospitalized adults with CAP and 241 controls without symptoms were prospectively enrolled. Urine samples were collected for pneumococcal urinary antigen tests and nasopharyngeal swabs for viral and bacterial analysis, combined with routine diagnostic care.

Results: Among the included CAP patients, Streptococcus pneumoniae was the most common pathogen, detected in 28% of patients, followed by Haemophilus influenzae in 16%. Viruses were identified in 28%, and concurrent viruses and bacteria were detected in 15%. There was no difference in mortality, length of stay, or symptoms at hospitalization when comparing patients with bacterial, viral, or mixed etiologies. Among the control subjects without respiratory symptoms, S. pneumoniae, H. influenzae, or Moraxella catarrhalis were detected in 5-7%, and viruses in 7%.

Conclusion: Streptococcus pneumoniae emerged as the predominant cause of CAP, followed closely by viruses and H. influenzae. Intriguingly, symptoms and outcome were similar regardless of etiology. These findings highlight the complexity of this respiratory infection and emphasize the importance of comprehensive diagnostic and treatment strategies.Clinical Trial Registration: ClinicalTrials.gov, identifier [NCT03606135].

Keywords: CAP; ECAPS; Haemophilus influenzae; Moraxella catarrhalis; Mycoplasma pneumoniae; community acquired pneumonia; influenza virus; lower respiratory tract infection.

Figure 1

Etiology of CAP within the cohort. In (A) the pie chart shows the proportions of microbiological findings in the whole cohort. A minor part (23 individuals only) was not tested for viral pathogens; 2.1% in the group with bacteria only, and 2.3% in the group “no finding”. In (B) the bars in the figure represent bacteria or viruses indicated on the x-axis. Some patients had multiple pathogens detected. The group “Other bacteria” (n = 5) includes Neisseria meningtidis, Fusobacterium nucleatum and Enterococcus faecalis, whereas group labeled as “Other viruses” (n = 18) consists of parainfluenza virus 1 to 3, adenovirus and coronavirus (OC43, NL63, 229E). The group “Enterobacterales / P. aeruginosa” (n = 10) includes Escherichia coli, Proteus Mirabilis, Enterobacter cloacae, Klebsiella pneumoniae and Pseudomonas aeruginosa. The group “Other streptococci” (n = 11) includes β-hemolytic streptococci and Streptococcus anginosus.