A used needle may seem like a strange souvenir to some, but to you it's a reminder of one of your closest brushes with death, in an adventure you've come to think of as:
The Vahzilok Plague
It all started when your contact informed you of a deadly new Vahzilok disease. Eager to help, you went into the streets and the sewers to collect data on the diseased Vahzilok. But your heroism was not without its price. You learned that you had been infected with the deadly Vahzilok plague.
Your contact sent you to Professor St. John-Smythe for a cure. But when you arrived at the professor's labs, you found them under attack. You defeated the Vahzilok inside and saved the professor's colleagues, along with some of the precious serum they had concocted. Grateful for your help, one of the scientists used this needle to administer the cure.
Restored to full health, you ventured into the sewers once more, this time on a mission to incinerate the contaminated bodies. You came face to face with Dr. Vahzilok himself, but the mad doctor was not able to prevent you from ridding the world of his plague.