Gotta say that's pretty fuckin brutal

The spread of fish tapeworm due to Roman conquest is well documented, and the only good explanation is garum. And I believe that larval cysts can survive pretty rough conditions, including high salinity.

The "right" way to get rid of them would be by heat, but you can't simply use cooked fish to make garum, it denatures the proteins required for the fish flesh to decompose "the right way".

But the most concerning part isn't even the parasites you're ingesting directly from garum. Sure, they'll get into your belly, and you'll become their definitive host. The problem is its offspring being literally shitted onto the soil, in a time where proper sanitation was non-existent; once you ingest their eggs, you're taking the role of the intermediate host, and they'll nest themselves across your flesh and brain.

History and Archaeology Online has some great introductory info.

Odds are that you won't find leftovers of those factories / workshops in the ruins of either Herculaneum or Pompeii though. Garum wasn't prepared in urban centres, as there were laws against it. (Garum production stinks really, really bad.) Instead it was prepared nearby, in areas with low demographic density, and then sent to the city for distribution.

And the region around Pompeii was great for that - it's coastal so you have access to fish, it's really sunny and garum fermentation is made under sunlight, and it's close enough to Rome to make travel times short.

The text I've linked mentions it, but 30% of the garum production of Pompeii and the surrounding region (Campania) was owned by a single guy, called Aulus Umbricius Scarus. He lived in Pompeii, got killed by the Vesuvius eruption, and his house has been identified.