Tissue-based SARS-CoV-2 detection in fatal COVID-19 infections: Sustained direct viral-induced damage is not necessary to drive disease progression.

ABSTRACT

Coronavirus disease 2019 (COVID-19) is an ongoing pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although viral infection is known to trigger inflammatory processes contributing to tissue injury and organ failure, it is unclear whether direct viral damage is needed to sustain cellular injury. An understanding of pathogenic mechanisms has been handicapped by the absence of optimized methods to visualize the presence and distribution of SARS-CoV-2 in damaged tissues. We first developed a positive control cell line (Vero E6) to validate SARS-CoV-2 detection assays. We then evaluated multiple organs (lungs, kidneys, heart, liver, brain, intestines, lymph nodes, and spleen) from fourteen COVID-19 autopsy cases using immunohistochemistry (IHC) for the spike and the nucleoprotein proteins, and RNA in situ hybridization (RNA ISH) for the spike protein mRNA. Tissue detection assays were compared with quantitative polymerase chain reaction (qPCR)-based detection. SARS-CoV-2 was histologically detected in the Vero E6 positive cell line control, 1 of 14 (7%) lungs, and none (0%) of the other 59 organs. There was perfect concordance between the IHC and RNA ISH results. qPCR confirmed high viral load in the SARS-CoV-2 ISH-positive lung tissue, and absent or low viral load in all ISH-negative tissues. In patients who die of COVID-19-related organ failure, SARS-CoV-2 is largely not detectable using tissue-based assays. Even in lungs showing widespread injury, SARS-CoV-2 viral RNA or proteins were detected in only a small minority of cases. This observation supports the concept that viral infection is primarily a trigger for multiple-organ pathogenic proinflammatory responses. Direct viral tissue damage is a transient phenomenon that is generally not sustained throughout disease progression.