forces sick so how do you know when it's okay and mehen you need to stay but from iran tonight, strong denials here's stephanie gosk. we begin with nbc's tom costello. >> reporter: the flu >> reporter: tonight, is upon us, that u.s. intelligence sources say satellite tenacious virus imagery and hanging in the air, communications lingering on door intercepts confirm handles and elevator iranian missiles sho buttons and co-workers a passenger jet out of are getting it the sky early tuesday the message from morning. doctors -- go home this video taken from the ground appears t show the moment a the reality 90% of missile exploded workers said they go the fireball streaking to work while sick across the sky 90. ukrainian airlines flight 752 left >> kate snow, kate teheran at 6:12 a.m. snow, quick question headed for kiev. for you. quick question >> what's up u.s. sources say two minutes later, two >> have you ever come to work sick russian-made missiles >> yes. fired at the plane >> yes, you have why? >> i have. because i had to -- seconds later, a because i had to work. midair explosion >> for shame, kate snow for shame! the plane crashing to the ground >> i don't want anyone to ever think i'm not actually sick when i'm u.s. officials believe leaving. the shootdown was an >> you worry that they accident as iran was think you're faking. on high alert for a >> yeah. u.s. counterattack >> we get too into our after firing missiles work and say today we at u.s. troops in iraq. have to keep on going. >> reporter: the cdc >> it was flying at a has some guidance. pretty rough if you have a fever neighborhood, and somebody could have 100 degrees or more stay home. made a mistake some people say it was don't come back until mechanical you've been fever free i personally don't for 24 hours and here think that's even a is a sensible question, personally. prevention tip.