Pathology of the swine-origin influenza A (H1N1) flu.

Pathological studies would aid in finding the real causes of death and in outlining adequate strategies for treatment regarding patients with poor clinical outcome of influenza A H1N1 swine flu. We describe the autopsy findings of six cases of influenza A H1N1 swine flu. The lungs in these cases had an alveolitis with hyaline membranes. Immunohistochemistry for influenza was positive only in lungs (in pneumocytes, in macrophages, in some multinucleate cells in alveoli, and in blood vessel walls) of two cases. Disseminated petechial brain hemorrhage was observed in four of the cases and focally in one case. Focal myocarditis was observed in one case. Coagulation infarcts (ischemic) were observed in the pancreas of two cases and in the spleen of two cases. Our results indicate that there was marked replication of the virus in alveoli in the more recently infected cases, which could explain the extensive diffuse alveolar damage. In our cases, there were important vascular phenomena that resulted in hemorrhage and thrombosis, but without marked decrease of platelet count and coagulation cascade disruptions. This would be attributed to hemodynamic disruption. However, it is possible that the hemorrhagic petechial lesions in the brain are due to vascular lesions or to an increase of endothelial permeability.