Ate your heat and humidy levels where they should be? If you are ending up with multiple BPs that have RI, you should definitely check your husbandry.

RI is not easy to transfer from one snake to the next unless they are in the same enclosure and drink from the same water bowl. It's the same as you having a sinus infection. You spread it by mucus and fluid that comes from your nose and mouth. Since snakes can't cough or sneeze, they need to share a water bowl or rub their face in the exact same spot that another sick snake has rubbed on and left nasal or mouth fluid behind.

So if your snakes keep getting sick and it's more than 1, you probably need to raise the heat and humidity. Cut out the possibility of drafts, and fix whatever else may be causing it.