First nosocomial cluster of COVID-19 due to the Delta variant in a major acute care hospital in Singapore: investigations and outbreak response. - Lim WY; Tan GSE; Htun HL; Phua HP; Kyaw WM; Guo H; Cui L; Mak TM; Poh BF; Wong JCC; Setoh YX; Ang BSP; et al. (The Journal of hospital infection, 2022)