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In Hong Kong, the first case of H7N9 was reported in an Indonesian domestic helper who visited Shenzhen in Guangdong in the last week of November 2013. What is H7N9? Influenza A virus exists in various forms, as differentiated by the specificities of their H and N antigens on the virus surface. These are denoted by numbers 1, 2, 3, 4…. Influenza A circulates widely amongst birds, for which the name "avian influenza" is derived. Avian influenza is classified into 2 categories by their propensity for severe disease in the host - low pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (LPAI). H5N1 has long been known as a cause of HPAI, which has led to deaths in poultry, and occasionally in human.

On 31 March 2013, the Chinese Government reported the first human cases of influenza A H7N9, an avian influenza virus. Most cases could be dated back to the first half of the year 2013, as illustrated in the map. A significant proportion of the reported cases developed severe diseases and some had died, a pattern not unlike that for H5N1. While H7N9 has not been previously reported in human, the H7 family has long been known to be associated with LPAI. Human infections with H7 (not H7N9) have been reported: In the Netherlands there was a cluster of 89 H7N7 cases in 2003, while sporadic cases have been reported in UK, Canada and USA over the years. There were scientific studies suggesting that H7N9 has originated from a reassortment of 3 virus strains that have infected birds. Generally speaking, the Influenza A family is a much more common cause of seasonal influenza than avian influenza in human population. In the winter season in 2012-2013, both H3 and H1N1(2009) were circulating in USA, while H1N1(2009) was the main influenza A virus detected in Hong Kong. For now, H7N9 is a new addition to our influenza world. Data for the H7N9 map were extracted from media reports.

香港首宗人類感染H7N9呈報病例發生在一名印藉家庭傭工身上,她2013年11月底曾經到過深圳。H7N9是什麼?它是甲型流感病毒多種亞型之一,病毒以表面的H和N特徵蛋白的號碼1, 2, 3, 4…命名。甲型流感病毒在禽鳥之間傳播,故此又稱『禽流感』。禽流感病毒一般分兩大類:高致病型和低致病型。H5N1是高致病禽流感病毒的一個例子,令家禽因病而死,偶爾感染人類並且引發嚴重疾病。

2013年3月31日,中國政府宣佈首次發現人類甲型H7N9流感,屬新禽流感個案,最早發病的追溯至同年2月中。地圖顯示確診者分佈華東一帶,不少人患重病甚至死亡,情況和過往的H5N1人類感染禽流感相似。雖然H7N9以前從未發生在人類身上,H7組別是已知的低致病型禽流感病毒。2003年,荷蘭發生89例人類H7N7感染群集,而英國、美國和加拿大等地方曾出現人類H7零星個案。最新科研結果顯示,H7N9可能源自三種不同的禽流感病毒基因重組。整體而言,甲型流感病毒引起的季節性流感比人類禽流感更為普遍。剛過去的冬季(2012-2013),H3和H1N1(2009) 都在美國廣泛傳播,而H1N1(2009) 則是香港的主流病毒。H7N9為流感病毒世界帶來又一新成員。地圖資料取材自不同的媒體報導。