This type of zombie is generally a result of disease experimentation gone very, very bad. Once infected with the disease, a fast zombie experiences a startling increase in strength and speed and aggression. They are able to cover a lot of ground very quickly. Running from a fast zombie is rarely an option...YOU WILL BE CAUGHT. If caught and ANY transferal of bodily fluids (tears, sweat, blood, saliva, semen, etc.) occurs, the disease will be transferred to you. Then you too become a fast zombie.
HOW TO KILL IT: The fast zombie is technically not an undead being. The best strategy is wait them out while they forget to feed themselves and starve to death. Unless they start feeding on the local rodent population...that's bad news. REALLY bad news. Government intervention through the use of massive property and collateral damage annihilation is the only answer.