It is the first time the H7N9 bird flu virus has been found in humans , although three other strainsin the H7 family - H7N2 , H7N3 and H7N7 - have previously been found in humans , but therewere no casualties .
这是人类首次感染H7N9禽流感，虽然之前H7亚型禽流感病毒（H7N2、H7N3、H7N7）已有人类感染病例发生，但并未出现死亡病例。
h7n7