What reason led to people with respiratory illness move to the American West

An analysis was conducted to determine the Worst Cities for Respiratory Infections to promote awareness to people concerning respiratory infections. And according to the surveys conducted, not only did the West region have the least cities on the list of the "The 50 Worst Cities for Respiratory Infections", but the American West is ranked eight out of the top ten cities wherein physicians noted and recorded the fewest respiratory antibiotic prescriptions for each individual in that area.