中國H7N9禽流感疫情之回顧

Review of the 2013 Avian Flu H7N9 in China

2013年3月中國公布世界首例人類感染H7N9禽流感後，至今已有百餘名病患受到感染。受感染者的年齡中位數為61歲，約70%為男性，近六成有活禽接觸史，據目前流病推估可能潛伏期為10天。患者最常見的症狀為發燒及咳嗽，血液檢查可見淋巴球及白血球低下，胸部X光中97%有肺炎之表現，其中54%影響雙側，89%為consolidation，56%為ground-glass pattern。最常見的併發症依序為肺炎、急性呼吸窘迫症候群、休克、急性腎衰竭及橫紋肌溶解症，約七成病患需住至加護病房、六成需使用呼吸器、近兩成患者需使用extracorporeal membrane oxygenation，從發病到死亡的平均為11～14天，平均恢復時間為18日，目前死亡率約32%。序列分析顯示H7N9病毒的八段基因需來自於禽鳥類，由歐亞候鳥帶來的H7病毒及N9病毒，而六段internal基因則源自雞的H9N2，藉由雞鴨作為中央宿主產生基因重組後再傳染給人。該病毒HA基因上的Q226L等突變使該病毒對於人類細胞的α-2, 6-linked sialic acid的結合力增加，NA stalk上五個胺基酸缺失則可加強病毒的複製且和陸禽間病毒的適應能力及傳播相關，H7N9具有多樣哺乳類流感病毒之特性，可以造成人類疾病甚至引起流行。目前該病毒仍以禽傳人為主，但不能排除有侷限性人傳人之可能。治療以抗病毒藥物及支持性療法為主，不建議使用類固醇，目前未有上市疫苗，預防方法為避免接觸禽鳥類及加強個人衛生，臨床及防疫上也應提高警覺及早偵測可能病例。

In March 2013, 3 urban residents in China were found to be infected with a novel avian-origin influenza A (H7N9) virus. More than 100 infected cases have since been reported in China. The median age of patients was 61 years, and nearly 70% were men. Further, 60% of the patients had a history of poultry contact. The estimated incubation period was 10 days. The most common symptoms were fever and cough. Neutropenia and thrombocytopenia were most often noted in hemograms. The most common complications were pneumonia, acute respiratory distress syndrome, shock, acute renal failure, and rhabdomyolysis. Pneumonia was found in 97% of patients by chest radiography, and consolidation and ground-glass patterns were noted in 89% and 56% of the patients, respectively. About 70% of patients were admitted to the intensive care unit. Further, 60% of patients required mechanical ventilation, and nearly 20% needed extracorporeal membrane oxygenation. The median time from the onset of illness to death or recovery was 11-14 days and 18 days, respectively. The mortality rate was 32%. Sequence analyses revealed that the H7N9 virus was a reassortant of H7, N9, and H9N2 avian influenza viruses from Eurasian wild birds, domestic ducks, bramblings, and chickens. This virus also has some mutations associated with mammalian receptor binding that increase replication and even transmission, such as Q226L substitution in the HA gene and 5 amino acid deletions in the NA stalk. These raise concerns of a pandemic. Anti-viral medication (e.g., neuraminidase inhibitors) and supportive treatment are the main therapeutic strategy for H7N9 infection patients. Treatment with corticosteroids is not recommended, and no vaccine is available thus far. Personal hygiene and avoidance of poultry contact are the most efficient preventions at present. Continuous monitoring of the epidemic and viral evolution as well as further studies of disease pathogenesis and transmission mechanisms will improve the clinical outcomes and contribute to outbreak control and measures against potential pandemics.