Epidemics are the result of any disease spreading through a population, they occur every year all around the world. Epidemics vary in severity according to how the disease spreads, and how severe the actual disease is.
Preparing for an Epidemic
Epidemics, like all disasters, require you to store food and water. Unlike other natural disasters they require you to make special considerations for medication, air filtering, isolation, and special suits.
Food should always be a part of disaster preparation, having sealed food set aside that you know is not contaminated could make all the difference if a severe epidemic hits. Having food also allows you to avoid visiting stores and risking exposure.
Water should always be on hand. During an epidemic tap water could be contaminated, or the supply could be interrupted entirely. Ideally you should have both storage and an alternative source such as a well or rain collection system.
Whenever possible you should acquire medication to have on hand, especially broad-spectrum antibiotics. If the epidemic is bacterial having antibiotics might be effective, however, antibiotics should only be used if you understand what you are doing. Vaccinations are also important, you should get every vaccination you possibly can. A virus cannot be medicated after you are infected, but if you have been vaccinated you are far less likely to contract the disease.
Positive Pressure Home Air Filtering
Being outside of a heavily populated area, while not always an option, will protect you from most disease. Epidemics spreads through various means, airborne, blood borne, direct contact, etc... Being outside of dense population will help protect you from all of these means of exposure.