AIDS

AIDS was a contagious, fatal disease (PROSE: Vampire Science) that spread on Earth sometime between the 1970s and the 1990s. (PROSE: Verdigris, The Taint) Sam thought of them, HIV tests and global warming as things that were regular features of her world but not Fitz Kreiner's, who'd come from the '60s. (PROSE: The Taint) Tom similarly remarked that the people of the '70s did not know of AIDS and other matters, so he had foreknowledge. (PROSE: Verdigris)

Peri Brown figured that the people on Reef Station One who were nostalgic about the 20th century and the early 21st had never heard of AIDS, Africa or Ronald Reagan. (PROSE: Synthespians™)

When Ferran read the Eighth Doctor's memories, he saw AIDS — along with multiple wars, rape, flooding mines, stock market crashes, concentration camps, anthrax and Agent Orange — as an example of evil on Earth. (PROSE: Father Time)