We propose to include studies that report the incidence of MH or provide prevalence data or the number of subjects with and without MH, from which the incidence can be calculated. Peer-reviewed, prospective cohort studies, retrospective cohort studies, cross-sectional studies, or reports issued by government organizations will be eligible for inclusion. Reference lists of included studies will be examined for additional relevant articles. No language or date restrictions will be applied. Non-peer-reviewed articles, review articles, case reports, case series, case–control studies, letters to the editor, commentaries, proceedings, laboratory science studies, and other nonrelevant studies will be excluded from analysis.