Sputum Culture results do not come back the same day. It takes at least 48 hours for the preliminary report; for example gram negative or gram positive bacteria. Then up to 5-7 days for the type of bacteria and sensitivities.. For example, sputum culture shows staph aureus and what antibiotic will work to kill it. Some sputum cultures can take even longer when looking for slow growing stuff. But in general, when my daughter has a sputum culture done I call after 6 days to know what she grew and what it is sensitive to.
Also, when my daughter is cultured it says on the order slip, patient has CF, the lab know how to handle these cultures. Once, my daughter had a culture done at her regular pediatrician's(can't remember why) It was back in 2 days and I do not think it was accurate.
Another thing; how did they obtain the culture? DId your child cough something up into a sterile cup? Or were they cough swabbed? My daughter has never coughed anything up into a cup. She just won't or can't. So they cough swab her, unfortunately this is not super accurate because it is not coming from deep in the lungs. So yes one could culture something in the lungs but not have it show up on culture because it was not obtained deep enough.
Hope you child continues to improve. My daughter is battling a blechy cough too
And i wonder if her last culture actually shows what it causing the problem..Time will tell. Hope I didn't confuse you.