Thank you all for your supportive words on my completion of year two! I really appreciate and value the online support I receive.
There are two main types of food sicknesses (and by sickness I mean gastroenteritis-like symptoms (vomiting, diarrhea, gas, bloating, cramps, aches, flu-like symptoms, etc)): food poisonings and foodborne illnesses.
Food poisoning - this is when bacteria has overgrown in the food and though its growth, they secrete toxins as byproducts of their metabolism. In short, the bacteria has deposited poisons into the food! When you re-heat old food in order to "kill of the bacteria", you really are able to kill the bacteria; however you cannot kill the toxins that have already been made by the bacteria with heat. This is why you can still get super sick from rice sitting in the fridge for a week, even though you microwaved it on high for five minutes. The rice may appear to be perfectly normal too (no mold in sight!), but that doesn't mean that it is full of bacteria and their toxins/poisons. You don't have to worry too much about these toxins because only if the food is old enough will the bacteria have had time to create enough toxins to make you sick and "poison you". An example of a bacteria causing food poisoning is E. coli.
Foodborne illness - this is when the bacteria has overgrown in the food or that a really bad bacteria has entered the food. Unlike food poisoning where it is the toxins that make you sick, in this case the bacteria itself is the one causing havoc on your body. Food borne illnesses are not quite as common because of our tendency to reheat leftover foods, killing off these bacteria, preventing us from getting sick. In the off chance that you don't store a food correctly (e.g. not refrigerated), don't prepare it safely (e.g. didn't wash hands after handling the egg shells), or don't cook it properly (e.g. heat meat to a temperature hot enough to kill bacteria lurking internally), then you may be exposed to bacteria to make you sick. An example of a bacteria causing foodborne illness is Salmonella.
Hopefully I haven't made you too worried! Obviously you're not getting food sicknesses everyday, so I'm sure you're all doing a good job of protecting yourself and your food. Some simple tips to remember are if it's meant to be cold, eat it cold! (E.g. keep that salad as cold as possible before you get a chance to eat it at lunch time) ...and if it's meant to be warm, eat it warm! (E.g. reheat leftover stew or Chinese take-out). Also, always take care with food prep. This is where the most contamination can occur. Wash hands when handling meat wrappings and egg shells as these are the things that haven't the biggest exposure to the "bad" bacteria. Eggs are actually sterile and bacteria -free (the shell keeps bacteria out!); the shells are the ones carrying the "bad guys".