Fig. 2

Left histogram shows the three indicators in sputum; HGF, cell-free DNA and index dip-test in the groups respiratory infection and controls. Right histogram shows the difference between groups in cell-free DNA concentration. The red circle separates the cases that had more severe symptom than the rest of patients. Values are expressed as median (min–max) and P ≤ 0.05 was considered as statistically significant. Significance is denoted as: *P < 0.05, **P < 0.01, ***P < 0.001 and ****P < 0.0001