Re: Sinus infection and Nasonex?
There is very little clinical evidence that Nasonex reduces one's ability to fight infections. For most people taking Nasonex at the recommended doses there amount that reaches the bloodstream is undetectable, which means it's not enough to weaken your body's immune system (oral steroids at higher doses taken over a long period of time can weaken the immune system but the amount that gets into your bloodstream is hundreds of times higher than what you would experience with Nasonex).
In all likelihood, your infection is being caused by the polyps blocking the normal drainage pathways in your sinuses, so dealing with the polyps will most likely address your infection as well. Unfortunately, very few people are successful in shrinking polyps with nasal steroid sprays - typically oral prednisone and/or surgery are required to address the polyps, with sprays like Nasonex helping to keep them from recurring.
Have you asked your doctor about a short course of oral steroids to help shrink the polyps?