“…18 Fifteen studies were conducted in Europe, 7,12,15,19,20,23,26,33,35,42,[49][50][51][52][53] three in Russia, 18,47,48 one in Japan, 30 and one in Africa. 38 Fourteen studies were performed in a single centre, 7,15,18,20,23,30,33,38,[48][49][50][51][52][53] and six were multicentre studies. 12,19,26,35,42,47 All studies had a cohort design, except three that were case-control studies.…”