Flu like symptoms after HD

My husband is a PD patient but is on temporary HD until he gets a new PD catheter. His temporary HD catheter has been in place for several months. About a month ago he started getting what I call flu like symptoms either during or just after his 4 hour HD. He starts off feeling really cold and then his temperature jumps up 5-6 degrees F. He also says his bones feel like they hurt. This lasts about 18-24 hours and then he feels OK. They tested for infection but nothing showed up.
Has anyone else experienced this and if so what was it casued with. As he only feels like this after HD I think it must be connected to his catheter but still no infection shows. Any help would be appreciated.

that’s a good question, I’m on Nocturnal hemodialysis, and sometimes I feel as if I’m coming down with the flu, symptoms as in chills and fever, yet
nothing shows up, (thank goodness) I would think that it’s possible that the system is sort of trying to get back to some kind of normalcy after treatment. But, it VERY important one gets checked out, this is just my experince and thought about it.