Microbiological etiology of aspiration pneumonia in Japan: Insights from a systematic review and meta-analysis

Abstract

Background

Anaerobic bacteria were historically considered the primary causative agent of aspiration pneumonia. However, recent studies suggest their role may have been overemphasized, and the microbial profile of aspiration pneumonia remains uncertain owing to diagnostic limitations. This study explored its microbiological epidemiology through a systematic review and meta-analysis.

Methods

We searched for English and Japanese articles published since 1990, evaluating the etiological bacterial species associated with aspiration pneumonia using PubMed and Ichushi-Web databases. The detection frequency (%) of each bacterial species was calculated using Review Manager and analyzed separately for Japan and other countries. Regional differences in detection of bacteria between these countries were also compared.

Results

This study included 21 articles: 14 from Japan and 7 from other countries. The most prevalent bacteria were Streptococcus pneumoniae (11.7 %, 95 % confidence interval [CI] 8.5–15.0 %) and Klebsiella pneumoniae (11.8 %, 95 % CI: 2.5–21.1 %), respectively. Gram-negative bacteria such as K. pneumoniae, Escherichia coli, and Pseudomonas aeruginosa were frequently detected, whereas oral streptococci and anaerobic bacteria were uncommon in both regions. Significant regional differences were observed in the detection frequencies of Staphylococcus aureus, S. pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.

Conclusions

This study highlights the bacterial profile of aspiration pneumonia and clarified the current understanding, showing that S. pneumoniae and gram-negative bacteria were frequently detected in aspiration pneumonia, whereas anaerobes and oral streptococci were less commonly identified. However, further investigation is needed to better characterize the bacterial spectrum, as a standardized definition of aspiration pneumonia and the pathogenicity of detected microbes remains uncertain.