There are many parasites that are microorganisms. Parasitic worms are not necessarily microscopic but are considered synonymous by epidemiologists.

I'm having a hard time finding peer reviewed studies about microorganisms and DE. However, on this website for DE it claims to kill bacteria as well as a long list of other benefits. [ https://diatomaceous.org/about/ ]

All in all, it doesn't seem that there have been many studies at all on DE and that much information is based upon anecdotal references.