Over one million Americans are living with the virus,out of an estimated thirty-three million people worldwide.
这句话也可以倒过来说...
Out of an estimated thirty-three million people worldwide,over one million americans are living with the virus.
在全球大约3300万人当中,有一百万的美国人已经感染病毒.（为强调后半句而倒过来,意思是一样的.）
Out of 在这里的意思,可以理解为：在...当中