Pathologic Studies of Fatal 2009 Pandemic Influenza A (H1N1) Virus Infection in the U.S.
WJ Shieh, DM Blau, P Adem, L Liu, A Schmitz, AM Denison, J Bhatnagar, M Deleon-Carnes, J Sumner, HA Jost, P Greer, C Smith, B Batten, T Jones, C Seales, L White, J Montague, J Bartlett, C Goldsmith, D Rollin, M Patel, SR Zaki. Centers for Disease Control and Prevention, Atlanta, GA
Background: On June 11, 2009, the World Health Organization declared the current circulating respiratory disease as an influenza pandemic, the first one in over 40 years. During the first four months after identification of a novel influenza A (H1N1) virus in the United States, over 500 deaths had been associated with infection by this virus. Pathologic studies on a series of fatal cases during that time are described in this report.
Design: Autopsy tissue samples with available clinical history and epidemiologic information were obtained from 77 patients with confirmed 2009 pandemic influenza A (H1N1) virus infection. The specimens were evaluated by an array of laboratory methods, including histopathologic examination, special stains, immunohistochemical assays (IHC), electron microscopy, and molecular techniques.
Results: Of the 77 cases, 36 (47%) were confirmed from specimens obtained at postmortem examination. The age range of the patients in this study was 2 months to 84 years with a median age of 39 years, and 81% between ages 20 to 60 years. Ninety percent of the cases included in this study had at least one underlying medical condition. Obesity (49%), cardiovascular disease/hypertension (30%) and asthma (24%) were the three most frequent pre-existing conditions in these patients. The most prominent histopathologic features were various degrees of diffuse alveolar damage. Type II pneumocytes and alveolar lining cells were the main targets involved in the infection. Thin-sectioned electron microscopy demonstrated extracellular viral particles in the alveolar space, associated with dense material. Co-infections with a variety of bacterial organisms were identified in almost one-third of the cases.
Conclusions: Our studies underscore the importance of performing autopsies and testing postmortem tissue samples in investigating 2009 pandemic influenza A (H1N1) virus infection. The most prominent histopathologic feature in fatal cases is various degrees of diffuse alveolar damage. RT-PCR and IHC assays are instrumental in establishing diagnosis and studying pathogenesis of this novel influenza virus infection. In addition, a combination of pathologic methods provides valuable diagnostic information to identify etiologic bacterial organisms as the source of co-infection.
Wednesday, March 24, 2010 1:00 PM
Poster Session VI # 219, Wednesday Afternoon