通常猪流感不会感染人类.美国历史上,每一两年在接触活猪的人群里会有一例感染.但从2005年12月到2009年1月间,人类感染猪流感病例上升了.这段期间出现12例病例.其中11例的病患有直接或间接活猪接触史;剩下这一例未知.这种病例上升可能和疾病报控系统完善有关,但疾病控制和预防中心CDC指出"猪流感病毒的基因变化和其他因素可能也有关系."这种新病毒与以往不同 ,它正在感染人类,世卫组织官员正密切关注其发展.

　　　　Do Humans Get Swine Flu?

　　　　Normally, swine flu bugs don't infect people. Historically, there's a case every year or two in the U.S. among people who have contact with live pigs.

　　　　But from December 2005 to January 2009 there was an uptick in swine flu cases. There were 12 human swine flu infections during this time. Eleven of these people had direct or indirect contact with pigs; in the twelfth case it was not known whether there was pig contact.

　　　　It's possible this uptick was due to improved reporting systems, but the CDC says "genetic changes in swine flu viruses and other factors might also be a factor."

　　　　The new swine flu virus is different. It's not yet clear that it's here to stay. But it is infecting humans, and that has world health officials keeping a close eye on it.