Katana

The Katana is a new close combat weapon revealed in Left 4 Dead 2. It kills Common Infected in one hit, (as seen in multiple game play videos) similar to other melee weapons. It has a much wider range than the any other melee weapon.

The katana is not really meant to be used against Special Infected, because using it on a Boomer would cover you in bile, and killing a Spitter would leave you right in the middle of the goo. Being used on a Charger, Jockey, Hunter or Smoker it would take time to reach them. Against a Tank or Witch it would do insufficient damage to stop them from counter attacking.

Trivia

 * The Katana is the primary weapon of Japanese Soldiers known as Samurai.