John Travolta's Alleged Hotel Germ Fears ... Uncover Grotesque Foot Wart

** WARNING -- YOU'RE ABOUT TO SEE SOMETHING ABSOLUTELY DISGUSTING ... BUT KINDA AWESOME. OKAY, YOU'VE BEEN WARNED **

So, we were talking to "House of Cards" actor Jimmi Simpson about a report that John Travolta will only stay in hotel rooms that have been vacant for 24 hours ... when something gross came up.

Not about John. Not about Jimmi. It was a revelation about the wife of a TMZ staffer who got a SUPER GNARLY virus on her foot while staying at a hotel in Paris.

Our very own Dax Holt decided to share an insanely graphic pic of his wife's foot after her 4th surgery to remove the Plantar wart ... and it's intense.

Don't worry, she's fine now ... but she'll never shower in a hotel without flip flops ever again.

... and neither should you!