Formula X (House of the Dead)

"At the height of the Cold War in either the 50s or the 60s, what the Americans and the rest of NATO wanted to fear the most and an alternative to nuclear weaponry in order to take out the Soviets and the rest of the Warsaw Pact by using Formula X, which would be intended to turn normal soldiers into superhumans. Well, that's all's well that ends well for the communists since this project had failed, so they'd guess that they'll have to hide it into an underground bunker. Would Papa Caesar be so responsible for a mutant outbreak in Bayou City?"

--Su Ji-Hoon, Papa Caesar Returns

Formula X was a mutagen developed for military purposes. Samples were hidden in an underground bunker, which was discovered by prison warden Clement Darling. His experimentation with Formula X caused a mutant outbreak in Bayou City, Louisiana.

In When the Cold Breeze Blows Away, it would be discovered in during USRAC War that Papa Caesar or Clement Darling would making their experiments or Formura X unidentified enemies

Therefore,Delilah Medici is the one who created the combination of T-Virus and Formula X named Formula T-Virus,which caused the Schadelerian Infection