MRSA感染が増悪に関与したと考えられたインフルエンザA型重症肺炎の１死亡例

A Case of Severe Influenza A Pneumonia induced by Methicillin-resistant Staphylococcus aureus

要旨

　患者は51歳，女性で，咳嗽と発熱で当院へ入院した．MRSAが，喀痰と気管支鏡による吸引痰から検出された．入院時の胸部X線写真では両肺の浸潤影を認めた．気管内挿管が施行され，人工呼吸が開始された．重症肺炎と診断し，IPM/CS，EM，VCMなどが投与され，一時陰影は改善した．入院11日目に異常影は再増悪した．ARDSと診断し，メチルプレドニゾロンのパルス療法を施行したが，両側の肺野の異常影は全肺野に拡大した．入院20日目に，呼吸不全で死亡した．死後の肺組織には，びまん性肺胞傷害が存在した．ペア血清でインフルエンザＡウイルス抗体価が32倍上昇したことから，ARDSの原因は同ウイルスであると診断した．MRSAがインフルエンザ肺炎を重症化する可能性があることに注意すべきである．本症例は，インフルエンザ肺炎に重複した細菌感染がウイルスと細菌の共同作用を誘発し，肺傷害を引き起こしうることを示唆している．

Summary

　We report a 51-year-old woman with severe influenza A pneumonia. She was admitted to our hospital because of a cough and fever. MRSA was isolated from both her sputum and intratracheal aspirates by bronchoscopy. Her chest x-ray on admission showed bilateral infiltrates. The trachea was intubated and ventilatory assistance was begun. IPM/CS, EM and VCM were administered under the diagnosis of severe bacterial pneumonia. This therapy seemed to be effective against the infiltrates. On the eleventh hospital day, an increasing pulmonary shadow was noted. We diagnosed ARDS clinically. Abnormal shadow spreading toward the bilateral whole lung field worsened despite treatment by methylprednisolone pulse therapy. The patient died of respiratoy failure on the twentieth hospital day. Histologically, diffuse alveolar damage was present in the lung. Our final diagnosis was ARDS induced by the influenza A virus, because the antibody titers of influenza A in paired sera showed a 32-fold increase. We should be aware that MRSA may be the cause of severe influenza pneumonia. This case suggests that the superimposed bacterial infections in influenza pneumonia can induce the synergistic effects of viral and bacterial pathogens to produce lung injury.