SARS-CoV-2 RNA load in the lower respiratory tract, viral RNAemia and N-antigenemia in critically ill adult COVID-19 patients: relationship with biomarkers of disease severity

Abstract

Background: Little is known about the comparative kinetics of SARS-CoV-RNA load in the lower respiratory tract and in blood compartment in patients admitted to the intensive care unit, and how these relate to biomarkers of COVID-19 severity. Methods: Seventy-three consecutive critically ill COVID-19 patients (median age, 65 years) were recruited. Serial lower respiratory tract (n=165) and plasma (n=340) specimens were collected. RT-PCR and lateral flow immunochromatography assay were used for SARS-CoV-2 RNA quantitation and N protein detection in plasma, respectively. Serum levels of inflammatory and tissue-damage biomarkers in paired specimens were analyzed. Results: SARS-CoV-RNA was detected in the lower respiratory tract of most patients (92%). Viral RNAemia and N-antigenemia were documented in 35.6% and 40.1% of patients, respectively. Viral RNAemia and N-antigenemia cleared at a faster rate than SARS-CoV-2 RNA in tracheal aspirates (TA). SARS-CoV-2 RNA load was higher (P<0.001) in TA than in plasma, and correlated significantly (Rho, 0.41; P<0.001). A modest correlation was found between SARS-CoV-2 RNA load in TA and plasma and levels of ferritin and lactose dehydrogenase (Rho≤0.3; P≤0.008) in paired serum specimens. Neither the dynamics of SARS-CoV-2 RNA load in TA and plasma, nor N-antigenemia detection rate differed between surviving and deceased patients. Yet, a trend towards a higher mortality was seen in patients with viral RNAemia (OR; 2.82; 95% CI, 0.94-8.47; P=0.06).