I was curious about when the N95/99/100 standard started, and while I was doing some reading, I discovered that the new standard was adopted in 1995 primarily in response to protecting workers against TB. Actually, that's not that long ago, when you think about it.

If you recall, there was an upsurge in infectious TB in the early 90's. Workers in the healthcare setting and also in jails/prisons were very concerned about their safety. Before then, it seems that surgical masks on the patients and workers were the norm, but workers were getting infected so the CDC came up with a new standard. Prior to that, masks were regulated primarily for situations like manufacturing or mining, so those standards didn't necessarily fit well to biological threats.

Anyway, if you ever search the medical literature on masks/respirators, you see TB mentioned a lot, and now you know why.