[Two patients with novel influenza A virus (H1N1) pneumonia treated with steroid therapy after an incorrect diagnosis of rapid progressive interstitial pneumonia due to the negative results of a rapid-antigen test].

We encountered 2 patients with novel influenza A (H1N1) pneumonia initially treated with steroid therapy after an incorrect diagnosis of cryptogenic organizing pneumonia and acute interstitial pneumonia, made because of atypical radiological findings and negative rapid antigen test results. After the patients were discharged, we performed reverse-transcriptase polymerase chain reaction tests for the presence of novel influenza A (H1N1); the results were positive, and we established the correct diagnosis of infection by novel influenza A (H1N1) virus pneumonia. Diagnostic clues included radiological findings similar to those of previously reported cases of novel influenza A (H1N1) virus pneumonia and an increase in similar cases due to the novel influenza A (H1N1) pandemic, suggesting that these 2 patients were also suffering from it. Similar cases of inappropriate treatment resulting from an initially incorrect diagnosis of cryptogenic organizing pneumonia or acute interstitial pneumonia may occur, and greater attention should be paid to accurate diagnosis.