translation.en: Humans in the developed world spend more than 90 percent of their lives indoors, where they breathe in and come into contact with trillions of life forms invisible to the naked eye: microorganisms.
translation.zh: 在发达世界生活的人们 一生中90%的时间都待在室内 他们在这里呼吸着、接触着 数万亿的肉眼看不见的生命形态： 微生物