We describe a case series of five patients with influenzalike illness with pneumonia and ensuing ARF who underwent OLB with subsequently confirmed diagnosis by RT-PCR testing for S-IOV infections. This report has some limitations. First, this study may not validate the importance of OLB in this population; however, it did provide information about this new disease. Second, it is difficult to compare our findings with those of others because to our knowledge no studies reporting an OLB in patients with S- The lung tissue score was obtained independently by two different investigators. The pathologic findings were graded according to a five-point semiquantitative severity-based scoring system: 0 = normal lung parenchyma; 1 = changes in 1-25%; 2 = 26-50%; 3 = 51-75%; and 4 = 76-100% of the examined tissue. IFN, interferon; TNFa, tumor necrosis factor a. IOV have been published. 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). Although each of these features is non-specific, their combined occurrence, together with positive serologic, microbiologic, and immunologic investigations and/or ultrastructural tissue examination enables the diagnosis of S-IOV infection to be confirmed, and is particularly useful in clinically suspicious cases that do not fulfill the WHO criteria or in clinically inapparent cases.