Microorganisms are everywhere. You may not see, taste, or smell them, but they hide on your body, in the air, on kitchen counters and utensils, and in food. The main microorganisms are viruses, parasites, fungi and bacteria.
Viruses are the tiniest, and probably the simplest, form of life.
They are not able to reproduce outside a living cell. Once they enter a cell, they force it to make more viruses. Some viruses are extremely resistant to heat and cold. They don't need potentially hazardous food to survive, and once in the food, they don't multiply. The food is mainly a transportation device to get from one host to another.