The number that matters is the absolute pore size. Per the CDC, a filter needs 1 micron or smaller to remove parasites and 0.3 micron or smaller for bacteria – and no filter removes viruses, which are smaller than any of it.
That is why filtration alone is not complete treatment, and why the order is filter first and then disinfect. The water page sets out which gap each method leaves; it is worth reading before choosing, because the three methods fail in different places and the differences do not overlap.