Regarding this topic, as a qualified chef (kinda) with food safety and other related qualifications, i can safely say if you are reheating food, its generally fine.

Points -

1: The food must be cooked to a temperature of 70 degrees celcius, otherwise you wont kill the bacteria.
2: If you left the pizza out int he open, id suggest throwing it away. Not worth the risk.

If your food was left in a refrigerated environment, or a sealed container or something, itll be fine. If not, chuck it