I have repeatedly submitted sputum samples and gotten the following response "The presence of 10 or more epithelial cells per low power field

indicates contamination with oropharyngeal flora making the specimen

unsuitable for processing." Why is this happening and what can I do about how I collect the sample to avoid having it contaminated? My pulmonologist told me it happens often and not to worry, but those samples aren't being evaluated for gram stain cultures which have revealed infections (not NTM's) in the past.

Thanks for anyone who has advice they can share.