Thanks for query,
There is no harm in consuming left over food.
Any prepared food have chance to get bacterial multiplication after 3=6 hours as per climatic condition.
If you reheat it by microwaving it or in oven after that time the bacteria kills but still the altered composition is harmful.
If you just keep that food in refrigaterator just after it is left then you can consume it afterwards but if it remains out side for more than 3=6 hours & then you micro it it is not advisable to consume it.
Food stuff if contaminated with Blood of HIV
person if consumed has no risk of infection.