So when does a pandemic become a pandemic?

Today the WHO uprated the swine flu alert to Level 4 which means it recognizes the ability of the infection to spread from human to human. This is a necessary step towards it becoming an established pandemic.

So what makes a pandemic a pandemic?

The word Pandemic is from two greek words which mean: 'pan' -all, and 'demos' - people. So a pandemic refers to all peoples. In infectious disease, a pandemic means an infection that spread among all people, implying a transnational or transgeographic spread. In practical terms a pandemic has first of all to be an infection. That there are homosexuals all round the world doesn't make it a pandemic. But HIV is a pandemic. Secondly, the infection is not limited to just one nation or one geographic location. In the case of the current swine flu, the infection is seen primarily in Mexico. The non-Mexican cases currently appear to originate from Mexico, hence the it has not really spread beyond Mexico. But the moment, Canada or the US, show cases that are spread locally, that would imply spread beyond Mexican borders. That would bring it closer to being called a pandemic.