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 it would probably do little damage.

According to the Game Informer Magazine the Katana, like the axe, can kill a Witch if you can place a shot to the back of her head.

Trivia

 * The Katana is the primary weapon of Japanese Soldiers known as Samurai.
 * It is unknown why the katana appears in places like The Highway, being such an antique weapon, unless a survivor brought the katana with him/her to defend his or herself.