Public health, preparedness and the World Health Organization response to swine flu in 2009.

was so special about this virus to induce a state of near panic? With all infectious diseases, the two key factors that determine how much damage is done are transmissibility, or the ability to spread, and virulence, or the ability to cause severe disease. A disease that is highly transmissible, like the common cold, spreads rapidly but is not considered an epidemic or pandemic because it is not a serious illness. It is annoying at most, and recovery is usually spontaneous. A disease that causes severe damage is much more of a concern. For example, gram negative septicaemia frequently results in death even when appropriate antibiotic treatment is attempted. But this is not considered an epidemic or a pandemic because of the low transmissibility of this infectious condition.