Temporal changes over time in sputum rheological parameters after SARS-CoV-2 infection in two patients with chronic cough

We report temporal changes in sputum rheological parameters after SARS-CoV-2 infection in two patients with chronic cough (71-year-old, male, sinobronchial syndrome; 80-year-old, female, cough variant asthma). Both patients complained of decreased cough-related quality of life and increased phlegm stickiness after infection. In parallel, their sputum showed decreases in linear viscoelastic region (LVR) parameters, such as viscoelastic modulus (G^∗), elastic modulus (G'), and viscous modulus (G″), and increased tack (tan δ/G'; tan δ = G″/G') compared to pre-infection levels. Rheological parameters, such as G^∗ and tack, took at least several months to return to almost pre-infection levels after recovery from COVID-19. Further studies are needed to determine whether the viscoelastic fluctuations seen in these two patients are common to patients with post-COVID-19 cough and whether their delayed recovery is associated with prolonged clinical symptoms. A sputum rheology approach may provide new insights into post-COVID-19 cough.