Sir,We thank Drs. Joob and Wiwanitkit[1] for their interest in our publication on organizing pneumonia (OP) as a pulmonary sequelae of swine flu.[2] They commented on the increasing interest in the pulmonary sequelae of swine flu in chest medicine[34] and the importance of the diagnosis of secondary OP after H1N1 infection. Imaging studies play a fundamental role in the evaluation of swine flu sequelae, as noted in the recent literature.[5678910]We were particularly interested in the comments regarding the tomographic pattern of lesions observed in swine flu.[1] Based on the current literature, they stated that “predominant peribronchovascular and subpleural distribution of the lesions, resembling OP, is common, and this finding can be observed regardless of the timing of computed tomography (CT) relative to the onset of symptoms”. We would like to highlight that although the imaging patterns of these lesions are similar, the histological findings differ according to the phase of disease evolution. Gill et al.,[11] described pulmonary pathological findings in 34 people who died following confirmed H1N1 infection. Sixteen of these patients died during the acute infectious phase (average time in hospital, 3.4 days) and showed only acute diffuse alveolar damage (DAD); seven patients died after an average hospitalization time of 11.7 days and showed acute and organizing DAD. Two patients who died during convalescence (average time in hospital, 31.5 days) showed fibrosing and organizing DAD. A recent study[12] examining the correlation between CT features and pathological findings in five fatal cases of H1N1pneumonia (mean time in hospital, 2.8 (range, 1-6) days] described the main pathological features of DAD with hyaline membrane formation, associated with various degrees of pulmonary congestion, edema, hemorrhage, and inflammatory infiltration. No evidence of OP was found in these patients, but one patient who died 28 days after the first hospitalization showed typical elongated fibroblast plugs filling airspaces, compatible with OP.[12]Limited published data regarding CT aspects during the recovery phase after H1N1 infection are available. In the early stages (1st week) of the disease, lesions correspond to the viral infection in most cases. However, a differential diagnosis between bacterial infection and secondary OP should be considered in patients with opacities persisting for more than 2 weeks. This consideration is extremely important for therapeutic planning.