Physical Properties of COVID-19 Acute Respiratory Distress Syndrome (ARDS) Sputum

Introduction: COVID-19 respiratory infections are associated with copious, adherent respiratory secretions that prolong chronic ventilation and contribute to the morbidity and mortality caused by the disease. To target thinning these secretions requires understanding the physical properties that contribute to these tenacious secretions. Methods: We received surrogate consent from 11 patients with COVID-19 ARDS to collect an undiluted tracheal aspirate obtained as part of routine care. All samples were frozen at-80C immediately after collection and heat inactivated at 65C for 30 minutes to render them noninfectious prior to further analyses. These were compared with sputum collected from 4 patients with Cystic Fibrosis and 15 healthy controls. Clinical phenotypes of COVID patients included ARDS severity, treatments related to sputum clearance, and patient outcomes including length of mechanical ventilation and mortality. Sputum was characterized for percent solids, double strand DNA, and hyaluronin content. Results: Sputum samples were collected from 11 patients intubated with COVID-19 ARDS, with aspirates sampled between 2-18 days into their course. 63% of patients had thick secretions described by respiratory therapy, 81% had moderate or severe ARDS, and 90% had prolonged mechanical ventilation > 14 days. We found that the physical characteristics of COVID-19 sputum are similar to CF sputum, with markedly higher percent solid, hyaluronin, and double strand DNA content than that seen in sputum from healthy controls (Figure 1). Conclusion: In this proof of concept study, we show the feasibility of measuring numerous physical characteristics of COVID-19 sputum. As expected, we found that percent solids, DNA content and hyaluronin were similar to the known thick secretions of CF, and markedly increased in comparison to sputum of healthy controls. We were unable to identify differences in outcomes in this small cohort, with collection of additional samples ongoing to improve power. Figure 1. Physical characteristics of COVID sputum are much more similar to CF than normal sputum.