>> i'll be swabbing you for flu. have you ever done this before? >> no. >> reporter: chloe tennant came to total access urgent care in of. louis complaining of flu- like symptoms. 15 minutes later, after a battery of tests, dr. paul hinrichs delivered the bad news. >> so your influenza a. is positive. >> how are you today? >> reporter: it's a common crosnosis these days across missouri and across the country. >> i've been doing this a long time, and i have never seen such a high concentration of flu cases all at one time. >> reporter: at this clinic, they've been seeing 1,000 hacking, sneezing, feverish e tients a day, about twice the usual amount. >> one minute you feel okay, the mxt minute or hour, you have acute onset of fever. it can be as high as 103, 104 sometimes. >> reporter: at st. louis children's hospital, they take no chances with visitors. we were outfitted with an isolation gown, protective gloves, and a mask before