What is the test for a prison official to be held liable in a tort action for failing to warn of the risk of serious harm to a patient?

In order for a prison official to be held liable, they "must both be aware of facts from which the inference could be drawn that a substantial risk of serious harm exists, and he must also draw the inference." Farmer, 511 U.S. at 837. Where a defendant should have been aware of the risk of substantial harm but was not, "the person has not violated the Eighth Amendment, no matter how severe the risk." Gibson v. County of Washoe, Nev., 290 F.3d 1175, 1188 (9th Cir. 2002) (emphasis omitted).