Microscopic What?

I have a friend that recently went to an eye doctor in Shanghai for treatment of an eye infection. The eye doctor diagnosed the infection as being caused by air pollution and to my friends increasing discomfort explained that Shanghai's air was full of coal dust, rubber bits and microscopic human fecal matter. I understand the coal and rubber but I want to know how the fecal matter gets into the air? On second thought, maybe I don't want to know. But that explains the funny taste of the air.

Tonight I was at a reception in the 50-story Bund Center looking out over Shanghai's skyline at dusk. Tall skyscrapers marched in lines down the parallel streets and disappeared into a fog in the mid-distance. The smog gave the metropolis a yellow, post-apocalyptic feel. I've seen this scene a thousand times from different vantage points atop Shanghai's skyscrapers but now I see it in a new light - a microscopic fecal matter sort of light.