I have lost several to salpingitis, have one with it currently. It's quite frustrating, actually. There is not very much good info out there. I don't think it has been much studied. There are some that say that treating with antibiotics if caught early has been successful, but my experience is that it's difficult to catch it really early since they hide it so well. I have treated several that I thought might be early enough, several antibiotics and combo's, I have not, sadly, had one recover. I don't think it's 'contagious' in the generally accepted sense. It's bacterial and somehow it manages to get into the oviduct. I have seem some discussion on whether a rooster can spread it, but it doesn't really seem to be the case. I've not had enough of them with it to think that is really happening. The vast majority of my cases have been hatchery birds bred for prolific laying, so genetics may play a role, or perhaps the laying daily, or nearly daily like they do leaves the oviduct open to more bacteria. My heritage breeds have been less susceptible to reproductive problems as a whole. When I lost my first bird to this I searched and searched for more information, and was disappointed with the lack of it and the lack of detail and useful help. This is one of the better articles:
https://the-chicken-chick.com/salpingitis-lash-eggs-in-backyard/
I'm sorry you have hens with this.
