*2.1. Study Design and Population*

This cross-sectional study was conducted from May to November 2020 through an online survey. Participants were enrolled among hospital personnel working in different medical treatment facilities and included physicians, nurses, and other employees (such as biologists, pharmacists, laboratory technicians, and office workers). According to Italian legislation, in order to reduce the number of SARS-CoV-2 infections in the workplaces, employers had the possibility, when applicable, to guarantee working from home for the most vulnerable subjects. Consequently, some office workers enrolled in the present investigation performed remote work.

Study subjects were recruited in two Italian metropolitan areas, namely Trieste (group N) in the North and Messina (group S) in the South of Italy.

Data were collected through an online platform recruiting subjects by spreading an invitation link. In order to increase the diffusion and validity of this sampling method, the invitation for the survey was sent to directors and coordinators, requesting them to spread it to their teams in a hierarchical line.

#### *2.2. Procedures and Measures*

The self-administered questionnaire was composed of two sections and took no more than twenty minutes to be completed. The first section investigated the sample's sociodemographic characteristics and work-related factors: gender, age, educational degree, marital status, number of children, profession, employment in COVID wards, number of contacts per week with COVID patients, remote working, and seniority. The second one comprised three standardized questionnaires: European Quality of life–5 Dimensions (EQ-5D), Athens Insomnia Scale (AIS), and Brief COPE.

The European Quality of life–5 Dimensions (EQ-5D) is a broadly used questionnaire developed in Europe to evaluate the essential quality of life components. This tool measures mobility, self-care, usual activities, pain/discomfort, and anxiety/depression through one question for each of the five dimensions. Throughout an algorithm, the given answers permit the calculation of the EQ-5D index, in which 0 is death and 1 represents perfect health. The EQ-5D questionnaire also comprises a Visual Analog Scale (VAS), measuring respondents' perceived health status, ranging from 0 (the worst thinkable wellbeing) to 100 (the best thinkable wellbeing) [29]. Specifically, the EQ-5D index value describes the health state, while the EQ-VAS gives information about individual health perception [30,31].

The Athens Insomnia Scale (AIS) is an eight-item questionnaire that reveals insomnia. The first five questions report the subject's nocturnal symptoms, while the last three items investigate the daytime impact due to sleep disorders. Each item is assigned a score from 0 to 3 according to a 4-point Likert scale (with 0 equivalent to "no problem" and 3 to a "severe problem"). The maximum total score is 24, which indicates the most severe insomnia symptoms. A cut-off of ≥6 represents the criterion for confirming insomnia symptoms [32].

The Brief COPE evaluates different coping strategies, both adaptation and maladaptation approaches. We used this tool to evaluate the stress response in a recent period ("situational-actual" version). The questionnaire includes 28 items, each assigned a score from 1 to 4 according to a 4-point Likert scale, divided into 14 factors, each consisting of two items. The 14 factors are Self-Distraction; Active Coping; Denial; Substance Use; Emotional Support; Instrumental Support; Behavioral Disengagement; Venting; Positive Reframing; Planning; Humor; Acceptance; Religion and Self-Blame [33].

#### *2.3. Ethical Issues*

This study was carried out in accordance with the Declaration of Helsinki's ethical standards. The study needed no formal approval by the local Ethics Committee, though a formal communication of study beginning was given (notification with request for acknowledgement). All the subjects who accepted voluntary participation in the survey provided informed consent. Participation was voluntary and without compensation.
