I assume you're referring to the -% poison resistance portion of the debuff, correct?
If so, it is displayed... It only lasts 4 seconds if the player using injected strike only has 100 poisoning and no Anatomy.
The duration is based on Poisoning & Anatomy skills.
Also, the poison resistance penalty doesn't affect your cap poison resistance, so more than likely most people won't be affected by it anyway due to over-cap resist.