2.3. cfDNA isolation from fluid and plasma samples

Fluid samples (3–500 mL) were collected in sterile containers and plasma samples (10 mL) in Vacutainer tubes (BD, Plymouth, UK). After a first centrifugation step (509 g, 10 min), the supernatants were transferred to a new tube and immediately submitted to a second centrifugation followed by cfDNA purification. The sediments of the first and second centrifugation, if present, were extended on slides, stained by hematoxylin and examined under a microscope. Purification of cfDNA from supernatants (1.2 mL) was performed with the QIAsymphony^® DSP Virus/Pathogen Midi Kit using a QIAsymphony robot (Qiagen), following the manufacturer’s instructions. Extraction was performed in duplicates; cfDNA was purified from two aliquots of fluid. The final elution volume was 30 µL per aliquot.