question: To estimate the hospital attack rate of coronavirus disease 2019 (COVID-19) and the stratified basic reproduction number (R0) of its causative agent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a hospital setting in Taiwan. A total of 138 healthcare workers (HCWs) in a hospital who were exposed to COVID-19 within a patient household (January 14 to March 7,2020) were divided into two groups, based on their exposure level. All HCWs received throat swab SARS-CoV-2 RT-PCR detection twice. Routine infection control policies included environmental disinfection, use of personal protective equipment (PPE), and hand hygiene per Taiwan Centers for Disease Control guideline. The estimated attack rate and the R0were calculated. Compared with the "low-risk" exposure group, the "high-risk" exposure group was less likely to have used partial PPE, and more likely to have had contact time &gt;1 hour, performed "aerosol-production" tasks, and developed symptoms during quarantine. None of the HCWs in either group acquired COVID-19. All HCWs wore surgical masks and performed routine environmental disinfection. Estimated R0was 1.46 and 0 for household and HCW models, respectively, implying that the index patient did not transmit COVID-19. Using masks may help prevent hospital-acquired COVID-19. © 2021 Society of Internal Medicine of Taiwan. All rights reserved.