Pathologic Findings in Novel Influenza A (H1N1) Virus (“Swine Flu”) Infection

Abstract

Although novel influenza A (H1N1) virus infection has assumed pandemic proportions, there are few reports of the pathologic findings. Herein we describe the pathologic findings of novel influenza A (H1N1) infection based on findings in 2 autopsy cases. The first patient, a 36-year-old man, had flu-like symptoms; oseltamivir (Tamiflu) therapy was started 8 days after onset of symptoms, and he died on day 15 of his illness. At autopsy, the main finding was diffuse alveolar damage with extensive fresh intra-alveolar hemorrhage. The second patient, a 46-year-old woman with alcoholism, was found unresponsive in a basement and brought to the hospital intoxicated and confused. Her condition deteriorated rapidly, and she died 4 days after admission. The main autopsy finding was acute bronchopneumonia with gram-positive cocci, intermixed with diffuse alveolar damage. The pathologic findings in these contrasting cases of novel influenza A (H1N1) infection are similar to those previously described for seasonal influenza. The main pathologic abnormality in fatal cases is diffuse alveolar damage, but it may be overshadowed by an acute bacterial bronchopneumonia.

2009 H1N1 Fatalities: The New Mexico Experience

“…Our study reviews the histopathologic features of these fatalities and how they differ in certain key respects from those reported in other states. Previously published studies addressing pH1N1 influenza histopathology have reported acute and/or organizing DAD in the majority of autopsied cases (74–100%) (11–15). In our series, only 2/12 (16.7%) decedents manifested DAD.…”

“…There have been a limited number of studies addressing the histopathologic features of pH1N1 influenza fatalities (9,(11)(12)(13)(14)(15). As with other forms of influenza, histologic manifestations are not specific.…”

Influenza A/H1N1 Severe Pneumonia: Novel Morphocytological Findings in Bronchoalveolar Lavage

“…Nakajima et al in 2012 described four autopsy cases of influenza A/H1N1 with a histopathological pattern of acute DAD who presented with influenza virus antigen-positive type II pneumocytes, perhaps indicating a direct role of the virus-infected cells in the acute alveolar damage [ 11 ]. No specific cytophatic effect or viral inclusion has been described so far at LM in lung tissue specimens during influenza pneumonia [ 1 ].…”

“…Several studies reported histophatological observations during influenza A/H1N1 2009 pneumonia: the major finding was diffuse alveolar damage (DAD) [ 1 – 4 ]. Type II pneumocytes were considered the main target of influenza A/H1N1 infection [ 5 ].…”

Pathological and ultrastructural analysis of surgical lung biopsies in patients with swine-origin influenza type A/H1N1 and acute respiratory failure

“…Although there are already many autopsy series with patients with H1N1 that can be used for comparison, the pathological findings at autopsy are modified mainly by the presence of associated co-infections and mechanical ventilation. [32][33][34][35][36][37][38][39] In summary, we have presented the pulmonary pathology in a confirmed and well-defined series of cases of S-IOV infection associated with ARF. The pathological features, in addition to necrotizing bronchiolitis and DAD, included the presence of multinucleated cells and intra-alveolar fibrin exudates (organizing pneumonia-like lesions).…”