Background
Coronavirus disease 2019 (COVID-19) has been spreading worldwide since the first outbreak in China, in December 2019. The Radiological Society of North America reported that consolidation, reserve halo sign, and other findings of organizing pneumonia were found in the late phase of COVID-191. In general, the treatment for secondary organizing pneumonia (SOP) is similar to that for cryptogenic organizing pneumonia (COP). The British Thoracic Society guidelines suggested a steroid pulse therapy (SPT) for some cases with fulminant COP2. On the other hand, a previous report showed that systemic corticosteroids delayed viral shedding and that they were harmful for other coronaviruses3. Therefore, a routine use of systemic corticosteroids is not recommended for viral infections at this time. However, some reports suggested that the steroid therapy might suppress a cytokine storm by COVID-194. One retrospective study showed that the treatment with methylprednisolone for COVID-19 reduced mortality in some cases4. SPT was assumed to be effective in the late phase for SOP with respiratory failure. This study aimed to investigate the efficacy and safety of SPT for patients with SOP and respiratory failure due to COVID-19.