The authors have requested that this preprint be removed from Research Square.


 The authors have requested that this preprint be removed from Research Square.


Background
Severe acute respiratory syndrome coronavirus 2 caused the ongoing coronavirus disease-19  pandemic, became the most important challenge for the health care settings worldwide [1][2][3]. The experience from the previous pandemic of coronaviridae family showed that frontline health care workers (HCWs) were at the highest risk of infection due to close contact with the infected cases, touching the contaminated surfaces and performing the high risk procedures in airway management [4][5][6][7]. Emergency medical technicians (EMTs) are among HCWs that may even be at higher risk, as they regularly face with both symptomatic and asymptomatic cases [8,9]. So EMTs have a high priority for protecting against COVID-19 and also they need additional transmission-based precautions [4,6,10]. Infected HCWs can increase the transmission risk and their absence from work can decrease the health services' performance which may cause a defect in the chain management of transmission. [4,6,10,11]. The World Health Organization (WHO) claimed that HCWs have the rights to access adequate personal protective equipment (PPE) supplies, training about infection control, personal hygiene, waste management, and etc. to decrease the occupational risk of transmission [12]. HCWs were recommended to use PPE like the surgical or N95 mask, gowns, shield in a correct order, and being trained about it.
Various studies showed that factors such as adequate supplies of PPE, adequate training and education about using the PPE, etc. played an important role to control such infections which signi cantly decreased the risk of transmission [13,14]. The goal of this study was to assess the role of possible factors associated with increasing risk of COVID-19 among EMTs.

Study design
This study was a case-control study conducted in Tehran, Iran. The implementation of the project was approved by the ethics committee of Tehran University of Medical Sciences (Code: IR.TUMS.VCR.REC.1399.323). To maintain the principles of con dentiality, all information was analyzed and reported anonymously. Participants entered the study with informed consent.

Study population
During 18 th February to 20 th April 2020, all con rmed COVID-19 EMTs based on the results of reverse transcriptase polymerase chain reaction (RT-PCR) and/or lung computed tomography (CT) scan were considered as the case group. The number of the control group was two times more than that of the case group, and were randomly selected among the healthy EMTs.

Data gathering
All the participants underwent phone interview and the data were collected in a checklist of two sections.
First section was about demographic data and basic information including age, gender, weight, height, working simultaneously in another healthcare center other than the EMS, history of at least one chronic disease, optional use of any drug or medical supplement as prophylaxis and smoking status. The participants were also asked about the number of EMTs involved directly in taking care of patients, a history of working with an infected teammate whose infection had not been con rmed and before his quarantine, a history of having a con rmed case as their cohabitant, the number of missions, and the daily work-time. The type of face masks including S (the surgical masks), N (the N95 masks), S & N, and E (the elastomeric respirator) used before entering the place where had a possible or con rmed case, the type of cloth including U (uniform), I (disposable, one-piece, waterproof protective cloth), G (gown), NW (disposable, one-piece, non-waterproof protective cloth), I-NW, G-NW, and I-G type used before entering the place where had a possible or con rmed case, and general precautions during their daily life (washing hands, social distancing, using masks in crowded places and etc.).
The second section was about evaluating PPE use precautions and assessing the risk of infection among EMTs who had a history of exposure to a possible or con rmed COVID-19 case. The participants were asked to ll out a seven-part questionnaire consisting of 43 questions, in which each item had zero (no), one (to some extent) or two (yes) score. This questionnaire was about access to PPEs, patients' care precautions, following the PPE precautions, do ng PPE correctly, precautions during the patient transfer, knowledge about disinfection process, and post-exposure measures. Appendix 1 presents the used questionnaire that was prepared by the WHO for such assessment [15]. The information of participants in the case group was based on the events that occurred two months before their diagnosis, and the information of participants in the control group was based on the events that occurred two months before the interview.

Statistical analysis
All the data were analyzed using SPSS version 24.0 (SPSS Inc., Chicago, IL, USA). The quantitative variables were described using the mean ± SD and the qualitative variables were described using the frequency and percentage of the data. The relation between the categorical variables was examined using the Chi-square test and Fisher's exact test. The relationship between quantitative variables among the groups was examined using the independent sample T-test. P-value < 0.05 was considered statistically signi cant.

Results
Among 1600 EMTs, there were 70 con rmed cases of COVID-19 during the study period. Four of them were excluded because they did not answer the phone call. Sixty-six con rmed cases and 148 healthy EMTs took part in this study (all were male). The baseline information of the participants is shown in table 1. Among all participants in the case group, 64 (97%) cases were quarantined at home (with a mean of 13.35±6.49 and a minimum and maximum of 3 and 32 days). Only 17 (11.4%) cases were admitted to the hospital with a mean duration of 0.52±2.02 days of hospital admission. The frequency of participants in the case group who underwent RT-PCR and lung CT scan were 31 (47%) and 59 (89.4%), respectively. Apparently, some EMTs underwent only one diagnostic test and others underwent two of them.
The frequency of participants in the case group having a con rmed case as their cohabitant before and after the infection was 6(9.1%) and 5(7.6%), respectively. Working simultaneously in another healthcare center other than the EMS, the optional use of any drug or medical supplement as prophylaxis, the history of at least one chronic disease, smoking status, age, BMI, the daily work-time and the daily missions' time had no signi cant difference among the two groups (p > 0.05). The case group was twice as likely as the control group to have the history of at least one chronic disease, and the presence of chronic disease increased the risk of infection 1.98 times higher (95%CI: 0.76 to 5.16) but the difference was not statistically signi cant (p > 0.05). any drug or medical supplement as prophylaxis in the control group was more frequent than the case group, but the difference was not statistically signi cant (p > 0.05).
The case group mostly had two EMTs involved directly in taking care of patients which signi cantly increased the risk of infection 6.5-times higher (95% CI: 3.36 to 12.55, p < 0.001). Working with a con rmed case teammate whose infection had not been con rmed at the moment and before his quarantine or isolation signi cantly increased the risk of infection 4.98 times higher (95% CI: 2.187 to 11.38, p < 0.001). Table 2 presents the PPE use precautions and self-care implementation in dealing with COVID-19 patients by participated EMTs. General precautions of daily life and the type of face masks used before entering the place where had a COVID-19 case had no signi cant difference among the two groups (p > 0.05). The percentage of using the S-type face mask was signi cantly higher and using the N-type face mask was signi cantly lower in the case group before entering the place had a con rmed COVID-19 case. The percentage of using the I, G, and NW-type cloths before entering the place where had a suspected COVID-19 patient was signi cantly higher in the case group. The I-type cloth was the most common cloth used in the control group and the NW-type cloth was the most common cloth used in the case group before entering the place where had a con rmed COVID-19 patient (p<0.05). Precautions such as seal check after wearing the mask (p=0.015), covering the hair with a medical hat (p<0.001), not using personal items such as jewelry and mobile phone despite protective clothing (p<0.001), avoiding contact with the outer surface of clothing while removing (p<0.001) were less considered in the case group than control group. The results also showed that in 4.8% of the case group "touch of face, eyes, nose and mouth" occurred during the patient transfer, but this percentage for the control group was 0.7%; although this item was not signi cantly different in the two (p = 0.166).

Discussion
In this study we assessed the possible factors associated with the increasing of the risk of COVID-19 among EMTs and the results showed that the type of used face masks (the surgical mask) and the type of used cloths (using NW (disposable, one-piece, non-waterproof protective cloth)) are correlated with the higher risk of COVID-19 in EMTs. Also, the number of missions and working time during the last two months are not correlated with such risk.
To choose the best PPE, the infection control organizations recommended choosing after evaluating the risk level of exposure [7]. PPE should provide appropriate protection to the mode of viral transmission and be simple to use, easy to remove without contaminating the users, and ensure the use of PPE in a correct order, and also there should be a checklist regarding donning and do ng of PPE. All HCWs were recommended completing a checklist at the end of day at work and the data should be reviewed by the supervisors [4,16]. Behavioral factors such as cough etiquette and adherence to the global health guidelines should also be considered during the management of a transmission [6]. The WHO recommended infection control strategies in the health care settings such as isolation of suspected and con rmed cases, applying standard precautions, and implementation of environmental controls. [10] A study compared the e cacy of different kinds of mask and the results showed that the surgical masks are low e cient in protecting 10-80 nm sized particles and the N95/FFP2 masks have at least 95% e cacy against 0.1-0.3 µm sized particles (size of droplet produced by coughing or sneezing is less than 5 µm) [11]. The surgical mask have 80% protection against droplet particles and the N95 have at least 95% protection against aerosols particles which showed that using the N95 mask decreased the prevalence of contaminated HCWs signi cantly [4,7,17]. There are too many controversies in terms of used mask type. For example, a study in Canada, conducted by Bartoszko et al., showed that the e cacy of the medical and N95 masks had no signi cant difference among HCWs [18]. A case control study conducted on HCWs of ve different hospitals in Hong Kong in 2004 reported that 72 HCWs were infected by SARS in the time of the study and wearing N95 or surgical masks had no role in this regard [16]. On the other hand, along with the results of our study, Seto et al. reported that the risk of SARS infection signi cantly decreased by using the N95 mask comparing to the surgical mask; However, because of its di culties, the N95 mask was used less than the other mask types [19]. However, a study stated that correct use of surgical mask is more effective than wrong applying the N95 mask [7]. The failure rates of more than 5% in the use of N95 mask may occur due to the inappropriate use of mask like not tting on the face [4]. Regardless of the quality of the lter materials, FFP-type masks may not provide reliable protection if the mask does not t tightly. A study stated that the correct use of a surgical mask is more effective than wrong applying a N95 mask [7]. The N95 mask is a ltering, negative-pressure face-piece respirator, and its performance is highly dependent on a tight face seal [20,21]; Unfortunately, the case group in our study had a signi cantly lower percentage of participants who performed seal check.
Most of the studies mentioned that education on donning, do ng, and other strategies on using PPE, were as important as adequate PPE supplies and could obviously decrease the cross-contamination. So training about the presentation of SARS disease, the routes of transmission, the appropriate use of PPE, and environmental factors became mandatory in a lot of hospitals [10,11,16,22].
In this study, we found that the higher percentage of the case group's participants signi cantly used accessories such as a watch, covered their hair with a medical hat, touched the outer surface of PPE during do ng, and etc. On the other hand, they were better in the PPE do ng in the correct order, adhering to precautions during the patient transfer, following the precautions while performing an airway management procedure. Our study showed that in cases where both of the EMTs were directly involved, the chance of being infected was increased. So in each mission only one EMT was directly in contact with the patient and evaluated him/her, and for the next mission the other EMT was directly in contact with the patient, by this way the frequency of exposure will be reduced.
On the other hand, due to the lack of equipment during large pandemics, the involvement of more people in providing direct patient care requires more PPE which lead to shortage of PPE in the system. Given that the history of the disease was higher in infected people than in non-infected ones, this difference was not statistically signi cant, which may be due to the low power of the study; Though all infected individuals were included in the study by the time of performing the project. It is better to identify the high-risk personnel during an epidemic and not assigning such missions to them as much as possible. On the other hand, the presence of a teammate before con rmation and quarantine increases the chance of infection by 4.98 times. Screening is very important in identifying the suspicious people.

Limitations
Due to the fact that the project was based on self-expression and retrospect, there is a possibility of bias on the part of the participants. As in this study, there is a possibility that there is a re-call bias. The validity and reliability of the questionnaire was not assessed. The participants in the control group did not do any diagnostic tests to check their health and because of the high prevalence of asymptomatic cases of COVID-19 reported in other studies, this may overestimate the e cacy of PPE and precautions [23].

Abbreviations
Emergency medical technicians (EMTs); coronavirus disease-19 (COVID-19); personal protective equipment (PPE); health care workers (HCWs); World Health Organization (WHO); reverse transcriptase polymerase chain reaction (RT-PCR); computed tomography (CT); S (the surgical masks); N (the N95 masks); E (the elastomeric respirator); U (uniform), I (disposable, one-piece, waterproof protective cloth); G (gown); NW (disposable, one-piece, non-waterproof protective cloth); Declaration Ethics approval and consent to participate: The protocol of the study was approved by the ethics committee of Vice-Chancellor in Research Affairs -Tehran University of Medical Sciences and the code IR.TUMS.VCR.REC.1399.323 has been assigned to it. To maintain the principles of con dentiality, all information was analyzed and reported anonymously. Participants entered the study with informed consent. Consent for publication: All the authors present their consent for publication of the paper.
Availability of data and materials: The dataset has been presented within the additional supporting les submitted in journal website.
Competing Interests: None declared.
Funding: This study was funded with a grant from Tehran EMS Center. The project was commissioned by the organization and the cost was paid to the contractor.
Authors' contribution: The conception and design of the work by MS, PS and PHS; Data acquisition by PHS, FD and SB; Analysis and interpretation of data by SB and EA; Drafting the work by SB, EA and FD; Revising it critically for important intellectual content by MS, PS, and PHS; All the authors approved the nal version to be published; AND agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work.