Torque Teno Virus Dynamics in Plasma and BAL of COVID-19 ARDS Patients With and Without ECMO

Extracorporeal membrane oxygenation (ECMO) is used to manage severe acute respiratory distress syndrome (ARDS) and is associated with immune modulation. Torque teno virus (TTV) has been proposed as a surrogate marker of immune competence, but it remains unclear whether ECMO influences TTV levels. In this exploratory, retrospective, single-center cohort study, TTV DNA was quantified by qPCR in 174 paired bronchoalveolar lavage (BAL) and plasma samples from 50 adults with COVID-19-associated ARDS. Plasma samples from 40 healthy blood donors were included as controls for baseline comparison. We compared TTV loads between ECMO and non-ECMO patients, assessed longitudinal trends, examined BAL-plasma correlation, and explored associations with mortality and secondary infections. Early plasma TTV in COVID-19 ARDS was lower than in healthy controls (3.20 × 10² vs 6.31 × 10¹ c/ml, p = 0.041). However, linear regression in log space showed significant growth in BAL and plasma TTV loads over time (R² = 0.1813 and 0.2720 respectively, p < 0.0001). Longitudinal BAL and plasma TTV loads were closely correlated (R = 0.8295, p < 0.0001) although BAL TTV loads were consistently higher (p < 0.001). Early BAL and plasma TTV loads did not differ significantly between ECMO and non-ECMO patients and showed poor discrimination for ICU mortality and burden of secondary infections. While TTV load showed compartment-specific and time-dependent kinetics in COVID-19-associated ARDS, it was not associated with ECMO status. Early TTV levels did not predict mortality or secondary infections, arguing against its use as a standalone biomarker in this setting.