[1] Natl Publ Hlth Inst, Dept Epidemiol & Hlth Promot, FIN-00300 Helsinki, Finland
[2] Univ Liverpool, Liverpool Sch Trop Med, Int Hlth Res Grp, Liverpool L3 5QA, Merseyside, England
[3] Cent Hosp N Karelia, Joensuu, Finland
[4] Univ Liverpool, Dept Publ Hlth, Liverpool L69 3BX, Merseyside, England