Fig. 3.

Geographical distribution of prevalence studies, 18 studies [15, 19, 30, 54–68] reported prevalence globally. Varying tiers of regional observation with some cross-coverage were reported, from municipal to national levels. Study targets, including their administrative level if not specific, consisted of, from approximately West to East longitude: Oregon, Washington State, Oklahoma, U.S.A, Iceland, Faroe Islands, Navarre, Vecchiano, Copparo, Vasterbotten County, Uppsala, Tampere, Kaunas, Tartu, Kuthar Valley, Hong Kong, Taipei, Okayama Prefecture. a World map with national boundaries, adapted from [69]. Countries highlighted correspond to sites in which prevalence studies were performed. b Bar chart of number of prevalence studies published by country. c Bar chart of number of prevalence published by continent. No studies were identified from South America, Africa, or Oceania