Mutual aid agreements: essential legal tools for public health preparedness and response.

Mutual aid is the sharing of supplies, equipment, personnel, and information across political boundaries. States must have agreements in place to ensure mutual aid to facilitate effective responses to public health emergencies and to detect and control potential infectious disease outbreaks. The 2005 hurricanes triggered activation of the Emergency Management Assistance Compact (EMAC), a mutual aid agreement among the 50 states, the District of Columbia, Puerto Rico, and the US Virgin Islands. Although EMAC facilitated the movement of an unprecedented amount of mutual aid to disaster areas, inadequacies in the response demonstrated a need for improvement. Mutual aid may also be beneficial in circumstances where EMAC is not activated. We discuss the importance of mutual aid, examine obstacles, and identify legal "gaps" that must be filled to strengthen preparedness.