Funding for this research was provided by:
Received: 9 August 2018
Accepted: 19 November 2018
First Online: 4 December 2018
: The study was approved by the Scientific, Bioethics and Biosecurity Committees of the Instituto Nacional de Enfermedades Respiratorias Ismael Cosío Villegas (INERICV); all participants received complete information about the study and provided informed consent. Protocol number <b>INERICV: B15–15.</b>
: Not applicable.
: The authors declare that they have no competing interests.
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