Concern about growing number of respiratory illnesses / 'Respiratory ailments not solely linked to bad air' / Respiratory illnesses remain 'elevated' throughout much of country: CDC / Respiratory illnesses picking up after holidays / Europe battles 'tridemic' of respiratory illnesses / New spike in respiratory illnesses across US sparks concerns / Uptick in respiratory illnesses across the U.S. / Respiratory illnesses are on the rise: How to protect yourself / Respiratory illnesses surging across the country / What you need to know about respiratory illnesses this winter