Both epidemic and pandemic refer to spread of infectious disease among a population.

Pandemic indicates larger number of people gets affected by the infection than epidemic, and larger area is affected. Pandemic affects global population while epidemic affects only few parts of a country.

Epidemic is when an illness or health related problem present in a population more than it should normally occur. In epidemic only several people show symptoms of a particular disease in certain regions. Population across the country can present with the infectious disease, but the concentration stays within the original cities, but the disease does not spread to other countries. The number of people who are affected stays more than it should be.

With pandemic the rate of infection grows exponentially and more cases start to show up other parts of the country itself or to different parts of the world. The rate of infection exceeds higher than that of an epidemic.

For example, when flu starts to affect all part of the Mexico, and people who travel from Mexico carry that type of flu to Canada and US. In small period of time more people are infected with flu in other parts of the world. Now, we call this ‘flu pandemic’ rather than ‘flu epidemic’.

A pandemic also can occur regionally if it involves more cases than a simple epidemic.

Summary:

Pandemic is defined when there is a growing number of population and all part of the world is affected by an infectious disease.

In epidemic an illness present in a population more than it should normally occur and only several people show symptoms in certain regions of the country.