4 Department of Pediatric Respiratory Medicine, Faculty of Medical Sciences, Hospital CRS El Pino, University of Santiago de Chile (USACH), Santiago, Chile.
5 Facultad de Medicina, Universidad Autónoma de Yucatán, Merida, Mexico.
6 Research Unit, Department of Paediatrics, "Virgen de la Arrixaca" University Children's Hospital, El Palmar, Spain.