Bill Gates recently divulged to his staff an interesting detail from his meetings with President Donald Trump: Gates says Trump repeatedly asked him about the difference between two notorious viruses, HIV and HPV.

Gates made the claim in video footage obtained by MSNBC host Chris Hayes. The video shows Gates speaking to staff at a recent meeting of the Bill & Melinda Gates Foundation, Gates' private charitable organization, according to NBC News.

Gates described two separate meetings with the president related to science and innovation. "Both times, he wanted to know the difference between HIV and HPV, and so I was able to explain that those are things that are rarely confused with each other," Gates said.

HPV, or human papillomavirus, is a group of more than 150 related viruses that infect different parts of the body. They're very common — it's estimated that 80 percent of people will get an HPV infection in their lifetime, according to the Centers for Disease Control and Prevention. Most infections go away on their own, but some can linger and lead to health problems, including genital warts and cancer. There are vaccines to prevent HPV infection.

Both viruses can be sexually transmitted.

Originally published on Live Science.