As journal's policies following issues were accepted as conflict of interest for reviewers:

• work at the same institution as any of the authors (or will be joining that institution or are applying for a job there);
• they are or have been recent (e.g. within the past 5 years) mentors, mentees, close collaborators or joint grant holders;
• they are or have been recent (e.g. within the past 5 years) co-author in an article (except studies like GlobalSurg);
  
• they have a close personal relationship with any of the authors.