Funding for this research was provided by:
Centers for Disease Control and Prevention (200-2006-18797, 200-2001-00133, 200-2011-41872)
Text and Data Mining valid from 2019-04-09
First Online: 9 April 2019
Compliance with Ethical Standards
: The authors have no conflicts of interest to disclose.
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this type of study formal consent is not required.
: Informed consent was obtained from all individual participants included in the study.