Impinging jet ventilation (IJV) system is promising to improve air quality in hospital wards compared with traditional mixing systems, while previously studied IJV systems for hospital wards were, in fact, personalized ventilation systems. This study investigates the cross-transmission of contaminants in a 4-bed hospital ward ventilated by one diffuser, including the impacts of occupants’ posture and mask, and to suggest low-risk positions for healthcare workers. A numerical model is established and validated to simulate the airflow and contaminant distribution in the enclosure. The results include: a) the supply velocity of 1.3 m/s and temperature of 18 °C maintains an overall thermoneutral environment; b) the supply diffuser creates an overall recirculated airflow though the ambient air velocity in most regions (93.8 % of the ward space) is lower than 0.1 m/s; c) the root mean square of velocity along the height is 0.003 m/s between lying and sitting conditions, and the root mean square of temperature is 0.16 °C, indicating the impacts of posture on velocity and temperature fields are ignorable; d) the transfer of lying patient-released contaminants is dominated by the recirculated airflow, while in the sitting cases, it is dominated by thermal plumes; e) healthcare workers are advised to position themselves opposite the supply diffuser for lying patients, and alongside the walls for sitting patients to reduce infection risk; f) exhaled contaminants flows upward straightly when masks are functioning well. These outputs indicate that the work position of healthcare workers should be adjusted according to patients’ posture. Display omitted •The exhaled contaminant transfer is governed by a 3D recirculation flow.•A very low horizontal velocity (e.g., 0.1 m/s) can spread contaminates far.•Patients’ posture has ignorable effects on temperature and velocity distribution.•Healthcare workers’ work position should change according to patients’ posture.