The opening passage of this episode reveals that the X-Files have been shutdown for 6 months.
Gillian Anderson has the record of appearing in the most episodes of the series missing only the following five: Mulder's solo episode 3 (1994) (although Scully is briefly referred to in the dialogue), Skinner's episode Zero Sum (1997), The Lone Gunmen's episode Unusual Suspects (1997), the flashback episode Travelers (1998) and Agent Doggett's solo episode The Gift (2001). An additional unique instance is Musings of a Cigarette Smoking Man (1996) where only the voice of Scully (and Mulder) is heard during the plot's present timeline. Scully does appear on screen briefly, but it's in a flashback scene edited from Pilot (1993).
The original script for this episode was a lot kinkier and revealed a lot more about blood fetishism. These elements however fell foul of the Broadcast Standards so they had to be toned down.
"Club Tepes" is named for Prince Vlad Tepes (the Impaler), the inspiration for "Dracula."