The study site was a provincial-level tertiary hospital in the Xinjiang Uygur Autonomous Region specializing in treating COVID-19 patients. The ESFHCWs who assisted this designated hospital were assigned from different hospitals in Zhejiang Province and specialized in providing emergency medical support. A medical team was selected as the study sample. Almost 300 HCWs from 63 different hospitals/institutions in Zhejiang Province were sent to the site within 3 days. Before this mission, they worked in different departments of health facilities, such as respiratory, infection, emergency, intensive care units (ICU), and hospital infection management departments. In responding to the sudden outbreak of COVID-19, China has worked to prevent both imported cases and domestic resurgences for almost 3 years. All HCWs in different departments have experienced repeated COVID-19 training and assessment and have relevant knowledge. All ESFHCWs participating in this emergency mission were trained and qualified in the COVID-19 Prevention and Control-Consensus Diagnosis and treatment of COVID-19 (9th trial edition) (11), including the selection of PPE, the wearing and removing of PPE, hand hygiene, isolation requirements, COVID-19 diagnosis and treatment, and other related content before coming to Xinjiang Uygur Autonomous Region. Intensive care professionals are required to have rich experience in treatment and nursing, and to be able to carry out treatment and nursing work independently. The selected personnel should have good will quality, a sense of responsibility, meet professional requirements, strong business ability, good health, and be able to undertake high-intensity medical treatment. Priority should be given to the experience of participating in the treatment of COVID-19. Unfortunately, considering the time urgency of this task, these selection criteria may not be well implemented, and these ESFHCWs may not fully meet the inclusion criteria.

The medical team was comprised a leader and a management team (medical group, nursing group, hospital infection management group, and logistics support group) and strictly implemented closed-loop management for ESFHCWs and hotel staff. Closed-loop management refers to point-to-point (hotel-hospital) docking, except for medical team members and hotel staff; i.e., there is no contact with other personnel or social activity tracking of a management approach. Each person lived in a single room. Medical, nursing, and hospital infection management groups are responsible for medical-related work, including routine medical services, body temperature monitoring, nucleic acid sampling, personnel transport, health education, and personal protection training in designated hospitals. The logistics support team is responsible for protecting lives and other materials. The hotel staff carries out the cleaning and disinfection of the internal and external environments (including the commuter bus), and the hospital infection group provides training guidance. The management team established a full-time accommodation manager to manage the 24 h access of residents.

ESFHCWs treated COVID-19 patients in five isolation wards of the designated hospital, including four general wards and one ICU. ESFHCWs implement reasonable scheduling and arrange rotation breaks. Each person enters the isolation ward once per day, and the working time is less than 4 h. These medical staff tested negative for SARS-CoV-2 nucleic acid for three consecutive days before entering the designated hospital and were provided with sufficient protective equipment. Additionally, they received unified training and assessment of infection prevention and control-related knowledge, such as wearing and removing PPE and occupational exposure disposal processes. Only after passing the evaluation, they could initiate working in the designated hospital. They were required to wear N95 respirators outside the hotel room and all other PPE (including protective coveralls, latex gloves, face shields, and shoe covers) before entering the hospital. Infection prevention and control training throughout working hours and daily supervision reminders were carried out through video surveillance during work. Throat swabs from ESFHCWs were collected daily for COVID-19. All HCWs were tested for COVID-19 every day.

This study used an electronic questionnaire administered to investigate WeChat platforms. The questionnaire consisted of basic information, work experience, and the SIPC of ESFHCWs. Basic information included sex, age, marital status, SARS-CoV-2 vaccination, basic diseases, taking drugs, whether infected with SARS-CoV-2, and time of infection detection. Work experience includes the original medical institutions level, academic major, educational background, professional titles, position, work seniority, department, and whether the hospital has anti-epidemic experience. The SIPC of ESFHCWs includes data on infection prevention and control ability (training received, awareness of infection prevention and control, wearing and removal of PPE, supervision, and remindings) and physiological and psychological status since arrival to the Xinjiang Uygur Autonomous Region (personal emotion, psychological pressure, appetite, sleep, defecation, and medication). The SIPC part of questionnaire with 29 questions was designed based on semantic differential (SD) scaling (12). Five selection intervals were set for each question, which was 1–5, with a total score of 145. The higher the score, the better the SIPC of ESFHCWs.

Approval from the ethical review board of the First Affiliated Hospital of Zhejiang Chinese Medical University has been granted (2023-KSL-230-01). Before the study, the leaders of this medical team had given the consent and agreed cooperation. Before answering the questionnaire, all potential participants were informed verbally and given a chance to ask questions. In accordance with the general data protection regulation, the participants have been informed of their right to withdraw at any time and of how their data will be managed. All questionnaires were self-filled by participants anonymously. All records were identified by a code number. All local databases were password protected. To ensure confidentiality, data shared with project team members were blinded to any identifying participant information.

Statistical Package for the Social Sciences (SPSS) 24.0, a statistical software package, was used for testing the reliability and validity test of the questionnaire, general descriptive statistical analysis, and generalized linear regression analysis. Shapiro–Wilk and a histogram were used to test the normality of the data in this study. Frequency (N) and percentage (%) were used as categorical variables. Means and standard deviations were calculated for numerical variables. The Mann–Whitney U test and Kruskal–Wallis H test were used for comparison of differences in the scores of ESFHCWs with different characteristics in terms of SIPC. Variables were considered significant at a p-value less than 0.05.

The Cronbach’s alpha for the questionnaire showed acceptable reliability (α = 0.778). Exploratory factor analysis was used for validity analysis with Kaiser–Meyer–Oklin (KMO) measuring 0.628 and Bartlett’s test of sphericity being significant (significant p < 0.001) and the cumulative variance interpretation rate was 74.641%, indicating that the research data had good structural validity.

Basic information on the study participants is presented in Table 1. A total of 269 ESFHCWs who responded to the questionnaire were included. The mean age of the participants was 33.4 years, ranging from 22–57 years. Higher percentage of women (72.1%) participated in the study than men, in which 37.92% of the ESFHCWs were married and 68 (25.28%) were from medical institutions below grade three. The nursing profession (73.6%) accounted for the largest proportion, and 192 (71.38%) of the participants had a bachelor’s degree. There were 240 (89.21%) professional titles, mainly intermediate and below. Most staffs were doctors and nurses (202; 75.09%). Over 78.44% of ESFHCWs had a work seniority of more than 5 years. More than 60% of ESFHCWs had worked in an ICU and respiratory infections and hospital infection management departments. Approximately half of the ESFHCWs were experienced in anti-epidemic support, 254 (94.42%) were vaccinated with three or more doses of the SARS-CoV-2 vaccine, 37 (13.75%) had underlying diseases, and 179 (66.55%) had taken drugs during their work. There were six ESFHCWs (2.23%) with nosocomial SARS-CoV-2 infection.

The average SIPC score of ESFHCWs was 125.39 ± 8.08. The data in this investigation did not conform to the normal distribution, according to the normality test. The results of Mann–Whitney U test and Kruskal–Wallis H test showed that there were statistically significant differences in the SIPC scores of ESFHCWs for anxiety disorder (Z: −1.73; p < 0.05), taking gastrointestinal (Z: 2.90; p < 0.05), anti-inflammatory, anti-asthmatic (Z: 2.61; p < 0.05) and hypnotic sedative (Z: 3.53; p < 0.05) drugs, academic major (Z: 2.20; p < 0.05), position (H: 9.80; p < 0.05), work seniority (H: 11.40; p < 0.05), and work experience in the hospital infection management department (Z: −2.34; p < 0.05). According to the results of the academic major, ESHCWs with anxiety disorder, and taking other medications (gastrointestinal, anti-inflammatory and anti-asthmatic, and hypnotic sedative drugs) had lower scores. The total score of infection prevention and control status of nurses (126.05 ± 7.80) was higher than that of doctors (123.55 ± 8.62). Compared with the full-time staff of the hospital infection management department and logistics support personnel (130.70 ± 8.45), the ESFHCWs with the position of ordinary doctors (122.76 ± 8.30) scored lower in the infection prevention and control status. Compared with less than 5 years of work seniority (122.74 ± 8.91), the ESFHCWs with more than 10 years of work seniority (126.96 ± 7.71) had higher scores. Being a ESFHCW with work experience in the hospital infection management department (133 ± 5.00) were found related to scoring significantly higher points from the questionnaire. Besides, the score of the six infected patients was 127.17 ± 6.80, no less than 125.35 ± 8.12 of the uninfected patients, and the difference was not statistically significant (Z: 0.42; p > 0.05).

Basic information on the six ESFHCWs with nosocomial SARS-CoV-2 infection, of which two were male doctors and four were nurses, is presented in Table 2. The mean age of the infected individuals was 29.43 years, ranging from 22–34 years. Three of them were from medical institutions below grade three. Four of the participants had undergraduate educational backgrounds. All the participants had intermediate and below-professional titles. Four had work experience in intensive care and respiratory departments, and two had no experience of anti-epidemic support. One patient with type 2 diabetes did not complete the booster dose vaccination. Half of the patients were taking hypnotic sedative drugs. The shortest infection time was only 1 day.

Generalized linear regression analysis was performed on the SIPC scores of ESFHCWs with different characteristics. The results are summarized in Table 3. Work seniority; anxiety disorder; and use of gastrointestinal, anti-inflammatory and anti-asthmatic, and hypnotic sedative drugs were the independent risk factors affecting the COVID-19 prevention and control scores of ESFHCWs. Compared with ESFHCWs with more than 10 years of work seniority, ESFHCWs with less than 5 years of work seniority [β: −0.040; 95% confidence interval (CI): −0.0596 to −0.0204] and 5–10 years of work seniority [β: −0.022; 95% confidence interval (CI): −0.0396 to −0.0044] had lower COVID-19 SIPC scores. These scores were higher in ESFHCWs without anxiety disorder [β: 0.201; 95% confidence interval (CI): 0.0775–0.3245] compared to those with anxiety disorder. And these scores were lower in ESFHCWs taking any gastrointestinal [β: −0.027; 95% confidence interval (CI): −0.0446 to −0.0094], anti-inflammatory, anti-asthmatic [β: −0.043; 95% confidence interval (CI): −0.0744 to −0.0116], and hypnotic sedative [β: −0.061; 95% confidence interval (CI): −0.1022 to −0.0198] drugs compared to those not consuming the abovementioned drugs.