Assessment of drivers of antimicrobial usage in poultry farms in the Mekong Delta of Vietnam: a combined participatory Epidemiology and Q-Sorting Approach by Truong, DB, Doan, HP, Tran, VK, Nguyen, VC, Bach, TK, Rueanghiran, C, Binot, A, Goutard, FL, Thwaites, G, Carrique-Mas, J, Rushton, J