Abstract: Background：The Omicron pandemic in Shanghai from March to May 2022 is very challenging for the emergency department to attach equal importance to emergency rescue and pandemic prevention and control. Objective：To explore the effect of bubble strategy on emergency rescue and pandemic prevention and control. Design：Observational study. Methods：During this pandemic period, the hospital is designed as a big bubble, and the emergency department is designed as a medium bubble. The buffer zone, resuscitation room, consulting room and observation room are designed as small bubbles. Based on "four zones, two channels and twice triage", the original layout and process of emergency department were modified. The four zones were as the following: a. the clean zone mainly included personnel living room and personal protective equipment (PPE) donning room; b. the potentially contaminated zone was set between the contaminated zone and clean zone, including PPE doffing room 1 and 2; c. the contaminated zone included the second triage area, waiting area, resuscitation room, consulting rooms and observation room; d. the highrisk contaminated zone included the first triage area and buffer zone. Two channels were clean and contamination channels. Twice triage referred to the initial screening at the entrance of the emergency department, and fivelevel triage after admission to the emergency department. The buffer zone was used for those who were diagnosed with critical illness but had a red health code and no negative nucleic acid test results within 48 hours. Level Ⅰ/Ⅱ patients with negative nucleic acid test results within 48 hours were admitted to the resuscitation room. Level ⅢⅤ patients with negative nucleic acid test results within 48 hours or negative onsite antigen test results were arranged to the consulting room. Patients who had negative nucleic acid test results on the day of entering the hospital and requirements for observation are admitted to the observation room. The second emergency room was set up as a backup emergency room when the major emergency department needed to be closed temporarily because of the presence of COVID19 infection patients. The bubble rupture plan was established. If a patient treated in the consulting room or resuscitation room was confirmed to be COVID19 infection, the first environmental sampling was performed at the exposure site to evaluate the degree of environmental contamination, and a second sampling was performed after terminal disinfection to evaluate the environmental safety. The second emergency room was activated if necessary. Main outcome measures：Nosocomial infection and occupational exposure of medical staff. Results：A total of 12 114 patients were admitted to the emergency department of our hospital, including 15 level Ⅰ patients, 310 level Ⅱ patients, 8 728 level Ⅲ patients, 2 564 level Ⅳ patients and 497 level Ⅴ patients. There were 7 major rescues, 32 medium rescues and 1 070 minor rescues. Fiftyeight patients were admitted to the PICU and 3 patients died in the emergency department. A total of 36 doctors, 38 nurses and 3 sanitation workers participated in the emergency department bubble, rotating every 5 days. Neither nosocomial infection nor occupational exposure occurred. Twentynine patients were admitted to the buffer zone, among which 3 patients were confirmed to be COVID19 infection and 3 patients were transferred to the PICU because of critical illness. In total, 652 patients were admitted to the observation room, among which 12 patients were transferred to PICU because of illness deterioration. Fiftyfive patients were guided to the COVID19 clinic by the initial screening, of which 4 patients were positive for nucleic acid test. A total of 6 patients with novel coronavirus infection were admitted to the emergency department. Among them, 3 children with positive nucleic acid test results were admitted to the consulting room, which caused environmental contamination. Terminal disinfection and environmental sampling were performed and the emergency department reopened when all environmental samples were tested negative. Conclusion：By adjusting the layout of emergency department and modifying the treatment process, it is possible to meet the needs of emergency care and pandemic prevention and controlat the same time, and to achieve the double zero of nosocomial infection and occupational exposure. The risk of bubble rupture existed, so it was necessary to make a plan.

Key words: SARS-COV-2, Nosocomial infection, Occupational exposure, Emergency department, Critical illness