Supplementary Material for: SARS-CoV-2 detection by digital polymerase chain reaction and immunohistochemistry in skin biopsies from 52 patients with different COVID-19-associated cutaneous phenotypes

Background: COronaVIrus Disease 19 (COVID-19) is associated with a wide spectrum of skin manifestations, but SARS-CoV-2 RNA in lesional skin has been demonstrated only in few cases. Objective: To demonstrate SARS-CoV-2 presence in skin samples from patients with different COVID-19-related cutaneous phenotypes. Methods: Demographic and clinical data from 52 patients with COVID-19-associated cutaneous manifestations were collected. Immunohistochemistry and digital PCR (dPCR) were performed in all skin samples. RNA in situ hybridization (ISH) was used to confirm the presence of SARS-CoV-2 RNA. Results: Twenty out of 52 (38%) patients presented SARS-CoV-2 positivity in the skin. Among these, 10/52 (19%) patients tested positive for spike protein on immunohistochemistry, five of whom had also positive testing on dPCR. Of the latter, one tested positive both for ISH and ACE-2 on immunohistochemistry while another one tested positive for nucleocapsid protein. Twelve patients showed positivity only for nucleocapsid protein on immunohistochemistry. Conclusions: SARS-CoV-2 was detected only in 38% of patients, without any association with a specific cutaneous phenotype, suggesting that the pathophysiology of cutaneous lesions mostly depends on the activation of the immune system. The combination of spike and nucleocapsid immunohistochemistry has higher diagnostic yield than dPCR. Skin persistence of SARS-CoV-2 may depend on timing of skin lesions, viral load and immune response.