Blood RNA sequencing was performed on a cohort of adults attending the Emergency Department with suspected infection who had subsequently-confirmed viral, bacterial, COVID19 and healthy controls

The cohort comprised patients recruited between Sept 2014- June 2020. It includes patients with bacteremia and positive viral diagnostic test in the context of acute admission. All patients with definite infection were used for signature discovery. Whole blood was collected at the time of recruitment in Tempus Blood RNA tubes and total RNA was isolated with the Tempus Spin RNA Isolation Kit (ThermoFisher Scientific) according to the manufacturer's instructions. RNA samples were stored at -80 °C until further analysis. After additional DNAse treatment, library preparation and sequencing of 30 million 150bp, paired end reads were conducted using the Illumina's TruSeq® RNA Sample Preparation Kit; ribosomal and globin RNA depletion was performed using the Illumina Ribo-Zero Gold kit and HiSeq 4000 at The Wellcome Centre for Human Genetics in Oxford UK.