Certainly you had the occasional medical practitioner drawing empirical conclusions that they couldn’t explain. "For some reason when I do this, I seem to have fewer complications with my patients / a higher success rate" would have been a not uncommon occurance, I’m sure.
The problem is, I doubt anyone would have noticed alcoholic beverages being noticeably cleaner in any way, because no one drinks purely just alcohol or purely just water. And with so many other possible vectors for contagion, even then it’d be hard to exactly pinpoint one factor over another as the cause with anything like certainty - meaning that at best, the “knowledge” of alcohol being cleaner than water would merely be seen as the unproven and unproveable hunch of certain individuals, not an accepted medical “fact”, as it were.
