Funding for this research was provided by:
National Institutes of Health (R24 AG032112)
National Institute on Aging (R01 AG049634)
Received: 14 February 2019
Revised: 12 February 2020
Accepted: 14 February 2020
First Online: 30 March 2020
Compliance with Ethical Standards
: The authors declare that they have no conflict of interest.
: This study received ethical approvals from the University of the Witwatersrand Human Research Ethics Committee and the Mpumalanga Provincial Research and Ethics Committee.
: 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 Declaration of Helsinki and its later amendments or comparable ethical standards.
: Informed consent (assent for minors) was obtained from all individual participants included in the study.