Effects of Contagious Respiratory Pathogens on Breath Biomarkers

Abstract

Due to their immediate exhalation after generation at the cellular/microbiome levels, exhaled volatile organic compounds (VOCs) may provide real-time information on pathophysiological mechanisms and the host response to infection. In recent years, the metabolic profiling of the most frequent respiratory infections has gained interest as it holds potential for the early, non-invasive detection of pathogens and the monitoring of disease progression and the response to therapy. Using previously unpublished data, randomly selected individuals from a COVID-19 test center were included in the study. Based on multiplex PCR results (non-SARS-CoV-2 respiratory pathogens), the breath profiles of 479 subjects with the presence or absence of flu-like symptoms were obtained using proton-transfer-reaction time-of-flight mass spectrometry. Among 223 individuals, one respiratory pathogen was detected in 171 cases, and more than one pathogen in 52 cases. A total of 256 subjects had negative PCR test results and had no symptoms. The exhaled VOC profiles were affected by the presence of Haemophilus influenzae, Streptococcus pneumoniae, and Rhinovirus. The endogenous ketone, short-chain fatty acid, organosulfur, aldehyde, and terpene concentrations changed, but only a few compounds exhibited concentration changes above inter-individual physiological variations. Based on the VOC origins, the observed concentration changes may be attributed to oxidative stress and antioxidative defense, energy metabolism, systemic microbial immune homeostasis, and inflammation. In contrast to previous studies with pre-selected patient groups, the results of this study demonstrate the broad inter-individual variations in VOC profiles in real-life screening conditions. As no unique infection markers exist, only concentration changes clearly above the mentioned variations can be regarded as indicative of infection or colonization.

Keywords: breathomics; metabolic profiling; pulmonary bacteria; real-time mass spectrometry; respiratory virus; volatile biomarkers.

Figure 1

Heat map showing relative differences in exhaled alveolar concentrations between groups. The selection criteria for VOCs are described in the Methods section. Relative differences were observed within and/or between different groups. As denoted through the numeric range between 0.0 and 1.0 within the color scales, red and blue colors indicate relatively high and low values, respectively. The heat map represents the group-wise mean of normalized (to corresponding maximum) concentrations of VOCs in seven groups (with subgroups based on disease symptoms) viz. healthy subjects (without any pathogens or symptoms); all cases positive for Haemophilus influenzae only, Streptococcus pneumoniae only, and Rhinovirus only; and all cases positive for H. influenzae + S. pneumoniae, H. influenzae + Rhinovirus, and S. pneumoniae + Rhinovirus, respectively. H. influenzae- and S. pneumoniae-positive cases are subgrouped based on the presence and absence of disease symptoms. The numbers of subjects (=n) in groups and subgroups are placed as numerical values. The x-axis represents the groups and the y-axis represents normalized concentrations of protonated VOCs (denominated by chemical formulas and molecular ions).

Figure 2

Comparisons of differences in VOC concentrations referring to queries Q1–Q13 of Table 2. Boxplots show exhaled alveolar VOC concentrations from different groups, subgroups, and corresponding room air. The x-axis represents the groups and the y-axis shows exhaled alveolar concentrations in ppbV. Statistical significances between groups and subgroups were tested by means of Kruskal–Wallis ANOVA on ranks with Bonferroni correction for pairwise multiple comparisons (p-value ≤ 0.05). Significant differences with respect to the healthy cohort are indicated by ‘#’. There were no statistical comparisons with room air concentrations.