Les,
The problem is that the hole size does not control if you get sick or not. Living organisms are soft. Even if they are .2 mm across some of them will get through a .1mm filter. It also depends on the design of the filter. It will vary for different designs using the same filter material. A single layer 1mm filter (a screen, in essence) will pass more than a .2mm x 1cm thick ceramic filter. The answer is to determine how much is removed. If it is enough, you will probably not get sick. That is why the important number is rejection rate.
Respectfully,
Jerry