Every parent knows the quiet, sacred routine of the midnight check. It is that peaceful moment when the rest of the world is asleep, and you walk on tiptoe into your child’s bedroom just to make sure they are warm. You pull the blanket a little higher around their shoulders, smooth back their hair, and smile in the dark. But lately, that peaceful routine has been broken by a sound that makes every parent’s stomach drop: a sudden, dry, hacking cough.

You stand there in the dim light, feeling a heavy knot form in your chest. Your immediate instinct is to check the windows. You make sure they are shut completely airtight to lock out the thick, gray city smog and the heavy traffic exhaust outside. You sit on the edge of their bed, rub their back until the coughing stops, and breathe a sigh of relief, believing that inside these four walls, behind a locked door, your family is safely protected by modern living.