Originally posted by unknowncapybara:

This happened to me the first time I played, too. Most likely, you've got an infected area somewhere that wasn't cleaned up or your Nugget(s) drank out of a lake. Either way, they got infected, the illness wasn't treated, and now you've got zombies.

As far as prevention, I've found that placing more reservoirs closer to Nugget residentials helps a lot, and then building multiple cemeteries as the city expands. You'll also want to check the range on them and keep an eye out for any Nuggets who might have died, just in case they wandered a bit trying to get resources.

When you're in the thick of it though, that's when it's kind of tough. You can sacrifice infected Nuggets at the temple for more creator points, though keep an eye on your happiness and fear meter, because if you don't counteract with placing a hospital or a recreation building, they might start rioting. If you have hunting lodges and your hunters are healthy, they'll hunt zombie Nuggets. You can also rack up a bunch of creator points, send everyone to a bunker (if you're able to), and when you release them, you can mass heal them as they walk outside. If you don't have a bunker and are in a bit of a bind, I've found that sacrificing one, doing a few mass heals, and repeating the cycle works okay.

Hopefully this is helpful!