The Editors-in-Chief have retracted this Article. Since publication, concerns were raised about the ethics and consent procedures for this study. We requested supporting documentation from the authors, including the application form submitted to the ethics committee and evidence of ethics approval. The documents supplied by the authors contain insufficient information related to the scope of the study for us to remain confident that the protocols complied with our editorial policies or are in line with international ethical standards (World Medical Association Declaration of Helsinki. Ethical principles for medical research involving human subjects ).
Caixa Li stated on behalf of all co-authors that they do not agree to this retraction.
 World Medical Association (2001) World Medical Association Declaration of Helsinki. Ethical principles for medical research involving human subjects. Bull World Health Organ 79(4):373