The A.N.T.S threat index uses a "low, medium and high rating system. It does not rate severity and is only for rating the chance of a threat occurring in the USA
A low rating
= 0 chance or rarely occurs - A medium rating
= can occur, but not on a regular bases - A high rating
occures daily or during normal seasonal cycles.
Top 15 Causes of Death - USA Life Expectancy.com
Threat level is high