A Case of Sudden Unexpected Infant Death with Presumptive SARS-CoV-2 Infection.

COVID-19 remains a challenge to the global healthcare despite the end of the pandemic, including due to the significant involvement of children in the epidemic process. During the pandemic period, an increase in the incidence of Sudden Unexpected Infant Death (SUID) and Sudden Infant Death Syndrome (SIDS) was observed. Currently, their rates remain elevated compared to the prepandemic period. The pathogenetic mechanisms underlying the fulminant course of infection in infants leading to fatal outcomes remain insufficiently understood. In this study, we report for the first time the results of histological and immunohistochemical examination of the lungs in a case of COVID-19-associated SUID in a 2-month-old infant. The absence of similar studies in the available literature limits opportunities for analyzing the pathogenesis of SUID. Our data allow a detailed characterization of the histological changes in the lungs, the localization and range of SARS-CoV-2 nucleocapsid protein expression, the identification of molecular mechanisms underlying apoptosis in the pulmonary microvascular endothelium, and the elucidation of the role of endothelial dysfunction. Particular attention in this article is devoted to the role of cytokines (IL-6, TNF-α, and IFN-γ) in the pathogenesis of hyperacute viral infection. The obtained data demonstrate substantial differences between the observed changes and the classic presentation of COVID-19 in older children. These findings offer prospects for improving prevention strategies and developing targeted therapy for fulminant forms of COVID-19, while also contributing to the understanding of SIDS pathogenesis.