Pathology and virology findings in cases of fatal influenza A H1N1 virus infection in 2009-2010

Aims: To describe the pathological findings, immunohistochemical localization of viral antigen and tissue reverse transcriptase polymerase chain reaction (RT-PCR) findings of different organs in cases of fatal H1N1 influenza virus infection from North India. Methods and results: Nine patients positive for H1N1 virus by a throat swab real-time RT-PCR (rRT-PCR) were included. Underlying risk factors included pregnancy, respiratory diseases, rheumatic heart disease, and chronic kidney disease. Pathological evidence of tracheitis, necrotizing bronchiolitis and diffuse alveolar damage was noted in all of the cases. Influenza viral antigen was observed by immunohistochemistry in the epithelium of the tracheobronchial tree, bronchial glands, gland ducts, and, less frequently, the alveolar epithelial cells. Viral particles were confirmed by electron microscopy in three autopsy cases. Tissue rRT-PCR for H1N1 viral RNA was positive in lung samples, but negative in other organs. Secondary bacterial pneumonia, cytomegalovirus infection and angio-invasive zygomycosis were detected. Conclusions: The pulmonary findings are similar to those described in past pandemics. Secondary fungal and viral infections, which have not been reported previously, were noted. Although the number of cases in this study is small, the findings reinforce the notion that changes in extrapulmonary organs are attributable to multiorgan dysfunction syndrome rather than a viral cytopathic effect, and that there is no transplacental transmission of virus.