An official website of the United States government
The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before
sharing sensitive information, make sure you’re on a federal
government site.
The site is secure.
The https:// ensures that you are connecting to the
official website and that any information you provide is encrypted
and transmitted securely.
Lyn-Cook R, Halm EA, Wisnivesky JP.Lyn-Cook R, et al.Prim Care Respir J. 2007 Aug;16(4):229-35. doi: 10.3132/pcrj.2007.00056.Prim Care Respir J. 2007.PMID: 17660889Free PMC article.