Traces of SARS-CoV-2 RNA in the Blood of COVID-19 Patients

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the third virus that caused coronavirus-related outbreaks over the past 20 years. The outbreak was first reported in December 2019 in Wuhan, China, but rapidly progressed into a pandemic of an unprecedented scale since the 1918 flu pandemic. Besides respiratory complications in COVID-19 patients, clinical characterizations of severe infection cases showed several other comorbidities, including multiple organ failure (liver, kidney, and heart) and septic shock. To better understand COVID-19 pathogenesis in different human organs, we interrogated the presence of the virus in the blood, or any of its components, which might provide a form of trafficking or hiding to the virus. By computationally analyzing high-throughput sequence data from patients with active COVID-19 infection, we found evidence of only traces of SARS-CoV-2 RNA in peripheral blood mononuclear cells (PBMC), while the virus RNA was abundant in bronchoalveolar lavage specimens from the same patients. We also devised a "viral spike-to-actin" RNA normalization, as a metric to compare across various samples and minimize errors caused by intersample variability in human RNA. To the best of our knowledge, the presence of SARS-CoV-2 RNA in the PBMC of COVID-19 patients has not been reported before, and this observation could suggest immune presentation, but discounts the possibility of extensive viral infection of lymphocytes or monocytes.