The phrase "respiratory tract" refers to the parts of our body that are involved in breathing. It includes our nose, throat, windpipe (trachea), and lungs. Full definition
(4) A review paper found that probiotic supplementation was able to significantly reduce the number of upper respiratory tract infections as well as reduce antibiotic prescription rates. (naturopathiccurrents.com)
This is especially the case when it comes to the prevention and treatment of upper respiratory tract infections. (mindbodygreen.com)
Clinical studies have proven that probiotics can decrease the rate of respiratory tract infections in children (Source). (healthadviceworld.com)