The prevalence of stress, anxiety and depression within front-line healthcare workers caring for COVID-19 patients: a systematic review and meta-regression - Salari, N; Khazaie, H; Hosseinian-Far, A; Khaledi-Paveh, B; Kazeminia, M; Mohammadi, M; Shohaimi, S; Daneshkhah, A; Eskandari, S (Hum Resour Health, 2020)