Postmortem findings in eight cases of influenza A/H1N1

In March and early April 2009, cases of a new swine-origin influenza A (H1N1) virus were diagnosed in Mexico and the United States. Influenza virus presents as a respiratory infection with high morbidity and mortality. We describe the postmortem findings of eight confirmed cases of influenza A/H1N1 in a medical examiner setting. The eight cases falling under the jurisdiction of the Harris County Medical Examiner (Houston, TX, USA) with confirmed influenza A/H1N1 infection between June and September 2009 were included in this study. All cases were males between 6 months and 54 years of age. All adult patients had a body mass index from 31 to 49.8 kg/m(2). Five cases had comorbid conditions including one case with sleep apnea and mental retardation, three cases with chronic ethanolism, and one case with thymoma, sarcoidosis, and myasthenia gravis. The remaining three cases had no pre-existing medical conditions. All patients presented with severe flu-like symptoms; yet, only five were febrile. Rapid influenza diagnostic tests were performed in three cases by primary-care physicians, two of which were negative. None of the patients received antiviral medication. The average disease duration time was 8.2 days (3-14 days). A wide range of histopathological findings including tracheitis, necrotizing bronchiolitis, alveolitis, intra-alveolar hemorrhage, and hyaline membranes, both in a focal and in a diffuse distribution, were identified. Influenza A/H1N1 viral infection presents with a wide range of histological findings in a diffuse or focal distribution; most consistently with tracheitis, necrotizing bronchiolitis, and alveolitis with extensive alveolar hemorrhage. These histopathological findings at autopsy along with a clinical history of flu-like symptoms should raise suspicion for influenza A/H1N1 infection, and postmortem analysis by the reverse transcription-polymerase chain reaction (RT-PCR) is recommended for an accurate diagnosis. Modern Pathology (2010) 23, 1449-1457; doi:10.1038/modpathol.2010.148; published online 27 August 2010