1 Department of Pediatrics, Cystic Fibrosis Center, The University of Alabama at Birmingham, 1600 7th Avenue South, Lowder 620, Birmingham, AL 35233, USA. Electronic address: hgutierrez@peds.uab.edu.
2 Department of Pediatrics, The Johns Hopkins Medical Institutions, Cystic Fibrosis Center, 200 North Wolfe Street, Baltimore, MD 21287, USA. Electronic address: pmogayze@jhmi.edu.