Metabolic alterations in pneumonia assessed by breath analysis: an exploratory paired longitudinal study comparing acute infection and post-recovery states.

Abstract

The diagnosis and monitoring of pneumonia remain a challenge due to its diverse etiology, overlapping clinical symptoms with other respiratory infections, and limitations in current diagnostic technologies for timely and accurate detection. We evaluated whether real-time secondary electrospray ionization-high-resolution mass spectrometry breathomics can capture pneumonia-associated breath-profile changes in a paired longitudinal cohort. In this single-center longitudinal study at University Hospital Zurich, Switzerland, adults with clinically confirmed pneumonia (n= 47, median age: 63) were enrolled between 2020 and 2023 sampled during acute infection and again after recovery (median interval 85 d). After pre-processing, 3635 mass-spectral features were retained across ion modes, and 1498 could be linked to at least one human metabolome database (HMDB) entry by accurate-mass matching (±1 ppm). Breath profiles were assessed using a subject-grouped, nested cross-validated partial least squares discriminate analysis (PLS-DA) and paired differential analysis. PLS-DA showed framework moderate exploratory internal discrimination between pneumonia and post-pneumonia measurements with moderate performance (median balanced accuracy 0.72; median AUROC 0.80;Q²0.24; two latent variables), with a permutationp-value of 0.112. Paired differential analysis identified 104 recovery-associated features (58 higher and 46 lower during pneumonia) meeting |mean log₂fold change| ⩾ 1 and FDRq⩽ 0.05, with putative accurate-mass matches to 239 HMDB accessions. Real-time breathomics captures reproducible changes in exhaled breath mass-spectral profiles from pneumonia to convalescence and reveals breath-profile heterogeneity not fully reflected by standard clinical indices. These results should be interpreted as exploratory and hypothesis-generating, motivating multicenter validation with tandem mass spectrometry-supported compound identification, clinically relevant control groups, and longitudinal outcome linkage.