Article History
Received: 6 December 2019
Accepted: 10 February 2020
First Online: 26 February 2020
Ethics approval and consent to participate
: All of the participants signed an informed consent before the analysis, and the study was approved by the ethics committee of Medical University Varna, No. 75. The obtained consent was written. Since none of the participants was minor, there was no need for parental consent.
: Not applicable since no personal information was used.
: The authors declare that they have no competing interests.