M2:TW: how to reduce Squalor?

How do I reduce Squalor in settlements in Medieval 2: Total War? Even the items that mention small-s squalor in their descriptions do nothing to alter the Squalor factor in the Population Growth and Happiness charts. Granted, these items to increase Health and/or population growth, but if there’s a way I could directly reduce just a small portion of the 45%+ Squalor factor in my Huge Cities it would make a huge different in the city’s happiness.

I’ve tried every building to try to increase trade, food availability, and health, but nothing seems to work.

One thing I didn’t realize right away is that if you don’t upgrade your cities’ size when the population increases, their squalor increases substantially. Build those bigger walls/larger castles as soon as you can.