Microsoft founder Bill Gates told his staff at the Gates Foundation, in a recently publicized video obtained by MSNBC, that he has had two meetings with Donald Trump since the president was elected.

Gates said he tried to persuade the president during both meetings to be a “leader who drives innovation.” Alarmingly, in both, Trump asked if vaccines weren’t a “bad thing,” said Gates, indicating that Trump believes in a conspiracy that has spread throughout the West in recent years, bringing back once-banished diseases like measles with it.

And both times, “he wanted to know if there was a difference between HIV and HPV,” Gates said, “so I was available to explain those were rarely confused with each other:”

Trump’s inattention to detail, lack of even rudimentary knowledge about American history, and fundamental ignorance about global trade is a constant in his presidency. But given his personal history, the fact that he doesn’t know or understand the difference between HIV and HPV is an almost unfathomable.

The first, human immunodeficiency virus (HIV) can lead to acquired immune deficiency syndrome, or AIDS. The second, human papillomavirus, is a virus that can lead to genital warts, and deadly cervical cancer for women. Both of them are sexually transmitted, but that’s where the similarities end—and at age 71, Trump should be well-versed on both.

For anyone living in Trump’s hometown of New York City in the late 1980s and through the 1990s (as he did) it was impossible to avoid the growing tragedy of the new disease AIDS. Deaths skyrocketed, and the city’s artistic community and the well-heeled socialites who helped fund it were devastated. Trump’s sister-in-law Blaine was a prominent fundraiser for charities for people stricken with the disease, as was his first wife (albeit after they divorced).

Among the early deaths was Trump’s attack dog lawyer and mentor Roy Cohn, a man whose loyalty Trump continued to praise decades later (paywall). However, while Trump stuck by Cohn through the early 1980s after he was disbarred for fraud—he “dropped him like a hot potato” when Cohn got AIDS.

HPV, meanwhile, is so common that about 80% of men and women get it at some point in their lives, according to the US Centers for Disease Control and Prevention; people who have had “multiple sex partners” are at the highest risk, the CDC says, or people whose partners have had multiple partners.

In men, the infection is “overwhelmingly subclinical,” meaning it doesn’t show readily apparent symptoms, so it has “resulted in a potentially large number of asymptomatic carriers.” In one study, 28% of men who visited a sexually transmitted disease clinic were found to be infected with HPV.

Several women in the adult entertainment industry have alleged that they have had unprotected sex with Trump since he married his third wife Melania in 2005. “You know, we talked about it, right beforehand,” former Playboy Playmate Karen McDougal told CNN about using protection during the “dozens” of times she had sex with Trump.

“He was starting to, and then he was like ‘I don’t like these things,’ ” she said, apparently referring to a condom. The two then discussed their mutual sexual history, and decided not to, she said.

Could Trump be one of the many men who carry HPV? There’s no known test for men, but the US has two recommendations to prevent its spread—using condoms and getting vaccinated.