RI is caused by humidity that is too low. However, a lot of people are under the misconception that humidity that is too high will also cause an RI. That is not (exactly) the case.
The only time a snake will get a respiratory infection from high humidity is when the humidity is so high that there is condensation in the enclosure. Basically, if there is no condensation, the humidity could be as high as 90%, it doesn't matter. Just so long as it doesn't drop below 50% and doesn't create condensation.
And the advice everyone has given is good - raise humidity, and maybe bump the temps up a touch too.![]()