Sulfureous Water Therapy in Viral Respiratory Diseases

The goal of this double-blind, interventional, randomized case-control, pilot trial is to evaluate the effects of active sulfurous (STW) versus placebo (SDW) inhalations on blood test parameters, serum inflammatory cytokines, spirometry data, as well as qualitative and quantitative changes in the nasal microbiome of subjects affected by long Covid. The main questions it aims to answer are: * if STW inhalations are effective on respiratory issues due to long covid compared to the placebo inhalation (SDW) * if STW inhalations are effective on long covid related fatigue issues compared to the placebo inhalation (SDW) * if H2S inhaled with STW is effective in modulating (decreasing) cytokines which are related to long covid cytokine storm compared to placebo inhalation with no H2S (SDW) * if STW inhalation modify nasal microbiome both from a qualitative and quantitative point of view respect to placebo inhalation (SDW) Participants will be randomly assigned to active inhalations (STW) or placebo inhalations (SDW) arm and subjected to 12 consecutive sessions of 20 minutes. Both arms will be tested for: * cytokines and inflammatory markers concentration (IL1b, IL6, ACE, GSS, S100B, Hs-CRP) * spirometry (resting, forced, DLCO) * exertion response (6 minutes walking test) * nasal microbiome sampling at visit 1 (enrolment), at visit 2(right after the inhalation treatment) and at visit 3 (3 months after treatment). Researchers will compare results reported by STW to those of SDW group to see if significative differences are detectable.