[1] Med Univ Sofia, Fac Med, Dept Epidemiol & Hyg, 2 Zdrave St, Sofia 1431, Bulgaria
[2] SofiaMed Univ, Multiprofile Hosp Act Treatment, Dept Med Oncol, 16 Dr G M Dimitrov, Sofia 1797, Bulgaria
[3] Med Univ Sofia, Fac Pharm, Dept Pharmacol Pharmacotherapy & Toxicol, 2 Dunav St, Sofia 1000, Bulgaria
[4] Natl Ctr Publ Hlth & Anal, 15 Akad Ivan Evstratiev Geshov, Sofia 1431, Bulgaria