Seroprevalence of SARS-CoV-2 Antibodies and Associated Factors Among Health Care Workers at the Departmental and Teaching Hospital of Borgou (Republic of Benin) in 2022

: COVID-19 is a contagious viral infection, responsible for a pandemic that started in China in December 2019. Health Care Workers (HCWs) have been particularly exposed to this virus. The aim of this study was to estimate the seroprevalence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) antibodies and predictors among health care workers at the Departmental and Teaching Hospital of Borgou (DTH-B). This was a descriptive and analytical cross-sectional study conducted from June 27 to July 27, 2022. Participants were recruited using a simple random draw from the list of HCWs in each hospital department. All participants gave free and informed oral consent to participate in the survey. A pre-established questionnaire was used to collect epidemiological and clinical data. Each participant received a rapid screening test for SARS-CoV-2 antibodies (Immunoglobulin [Ig] G and M). STATA/MP 14.1 software was used for data analysis. A total of 139 HCWs participated in the survey. The sex ratio was 0.51 and the mean age was 40.48±9.12 years. The SARS-CoV-2 antibodies seroprevalence was 92.02%. Eighty-six participants (63.70%) had received a complete COVID-19 vaccination and 135 (97.12%) had received at least one dose of one of the available COVID-19 vaccines in Benin. A history of confirmed COVID-19 was recorded in 31 participants (22.30%). Hospital exposure of confirmed COVID-19 cases was noted in 104 (74.82%) participants. Family exposure was noted in 18 (12.95%) participants. Factors significantly associated with SARS-CoV-2 antibodies positivity in multivariate analysis were female gender (p = 0.001) and complete vaccination against COVID-19 (p = 0.002). The SARS-CoV-2 antibodies seroprevalence among HCWs was as high as the vaccination coverage in the departmental and teaching hospital at Borgou. It would reflect the joint effect of significant exposure to the virus and the effectiveness of the COVID-19 vaccines.


Introduction
On March 11, 2020, the World Health Organization (WHO) declared the start of a global pandemic (WHO, 2020). It is the infection with the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) named COVID-19 (WHO, 2019). As of January 13, 2023, 662 million confirmed cases and nearly 6.7 million deaths have been reported worldwide (WHO, 2023). This pandemic started on the African continent on February 14, 2020 in Egypt (Gaye et al., 2021). Since the first case was reported in Benin on 16 March 2019, the cumulative toll published by the government of Benin on January 15, 2023 is 27,992 confirmed cases and 163 deaths (GRB, 2018). It has put a strain on all health systems, including in high income countries, due to high morbidity and mortality rates, forcing each health care system in affected countries to adapt rapidly (Armocida et al., 2020). It has been observed that many inpatient and outpatient services dedicated to other diseases have slowed down. This is the consequence of the saturation of hospitals, the contamination of personnel and the redirection of human and financial resources to the management of COVID-19.
Health Care Workers (HCWs) on the front line of the response are faced with an enormous workload due to the increase in hospitalizations and the limited capacity of health facilities to manage patients (Erdem and Lucey, 2021). They are thus inevitably exposed to the virus and are two to three times more likely to be infected than the general population (Dubost et al., 2020;Amnesty International, 2023). In a recent study, Amnesty International estimated that more than 7,000 HCWs have died from COVID-19 (Amnesty International, 2023).
In Benin, several measures have been taken in all hospitals in the country to limit the spread of the virus. This is the case of the Departmental and Teaching Hospital of Borgou (DTH-Borgou), a reference hospital in northern Benin. These included systematic screening of all new admissions, screening by Polymerase Chain Reaction (PCR) of all suspected cases, both among hospitalized patients and new admissions, as well as among HCWs, whether symptomatic or not, the provision of personal protective equipment to HCWs and the requirement that all hospital users wear masks. Other measures such as physical distancing, hand hygiene, education of hospital users and the general population whose effectiveness has been demonstrated in India through mathematical models have also been deployed . In spite of all these measures, many cases of COVID-19 were identified among the HCWs of the departmental and teaching hospital of Borgou. This would indicate that the virus has spread widely within this hospital.
Due to international collaboration, several vaccines against COVID-19 have been developed. Benin, through the COVAX facility, received its first doses on March 10, 2021 and made vaccination of HCWs against COVID-19 mandatory by a decision taken by the council of ministers on September 1 st 2021 (GRB, 2018).
It is in this context that the present study was initiated and aimed to assess the seroprevalence of SARS-CoV-2 antibodies among HCWs of the DTH-Borgou and to identify the associated factors.

Type of Study
This was a descriptive and analytical cross-sectional study conducted from June 27 to July 27, 2022.

Study Population
The study population consisted of all HCWs on duty at DTH-Borgou.

Selection Criteria
Health care workers of all categories, on duty at the DTH-Borgou during the study period, who gave their free and informed oral consent to participate in the survey, were included. Any HCW who interrupted the survey for any reason were excluded.

Study Variables
The dependent variable of the study was the result of the SARS-CoV-2 rapid diagnostic test . This test detects IgM or IgG. The test is positive when IgG and/or IgM are positive and negative when both IgG and IgM are negative.

Sample Size Estimation
The minimum sample size was calculated using the Schwartz formula as follows.
The minimum size of our sample was calculated by the Schwartz formula.
With: n = Sample size p = The seroprevalence of SARS-CoV-2 among nursing staff in a university hospital in Turkey was determined to be 7.4% (Omrane et al., 2021)

Sampling Technique
This was a random sample. Subjects were randomly recruited from all hospital wards from the HCWs rosters with weighting based on the size of the nursing staff in each ward.
The list of HCWs by category for each department was obtained from the DTH-Borgou human resources department. Then a rule of three was applied to determine the minimum number of staff xx to be recruited per department. The lists of all categories of HCWs per department who met the inclusion criteria were then drawn up in alphabetical order and numbered from the first to the last. We proceeded to a random draw without discount from each list using small paper coupons on which these numbers are written. Once the list of personnel to be surveyed by service was known, a daily schedule was established, taking into account the days of on call and duty of each subject to be surveyed. We then approached them to investigate them. In case of unavailability, or non-consent of a subject retained for the survey, a new random draw without discount was again carried out to replace the latter.
Initially, we obtained a list of healthcare worker by category for each department from the CHUD-B/A human resources department.
Application of the rule of three to determine the minimum staffing xx to be recruited per department. Or: with: EX = The number of healthcare personnel meeting the inclusion criteria by hospital department A = Total of all healthcare worker meeting the inclusion criteria of the different departments involved in this study Xx = Minimum size of staff to be recruited per department n = 139 represents the sample size for this study calculated according to the Schwartz formula where Xx = (Ex *n)/A Table 1 shows the summary of the results of the sampling technique, specifying the number of participants per department.

Data Collection
Data were collected during a face-to-face interview using a pre-designed questionnaire. The pre-test of the tools was done before starting the survey. Data collection was carried out in two stages. In the first stage, with the oral and informed consent of each participant, the interview allowed the variables defined above to be filled in. In the second stage, the rapid screening test for SARS-CoV-2 was performed, looking for immunoglobulin G (IgG) and/or M (IgM).

Validation of the Serological Test
The BIOSYNEX COVID-19 BSS (IgM/IgG) rapid test was performed in this study to determine the presence of SARS-CoV-2 antibodies in the respondents. According to the manufacturer, the IgG sensitivity of the test was 100% and the IgG specificity was 99.5%. The IgM sensitivity of the test was 92.6% and the IgM specificity was 99.2% (BIOSYNEX, 2023).
A compared study of five new SARS-CoV-2 whole blood finger stick IgG/IgM combined RDTs found a sensitivity of 95.8% and a specificity of 98.1% for BIOSYNEX COVID-19 BSS (IgG/IgM) test (Péré et al., 2021). In addition, a study found that after 15 days after symptom onset, BIOSYNEX test combining IgM and IgG detection showed the best performances (Velay et al., 2020). Thus, the test used in this study provides an assessment of the respondents SARS-CoV-2 antibodies seroprevalence.

Data Analysis
At the end of the data collection, the forms were manually analyzed to verify the completeness and consistency of the data. Data was entered twice in the French version of epi data 3.1. The data were cleaned and analyzed using the STATA/MP 14.1 statistical software. A descriptive analysis of the variables under study was performed. Thus, for the qualitative variables, the frequencies and proportions were determined. Comparisons were made using the Chi2 test or exact test if the expected value is less than 5. For the quantitative ones, the means with their standard deviation, medians, minima and maxima were described. To determine the associated factors, the logistic regression model in bivariate and multivariate analysis was used. This provided measures of associations, Odds Ratios (ORs) and their confidence intervals, p-values associated with Wald chi2. The threshold of significance was 5% and confidence intervals were calculated at 95%.

Ethical Considerations and Good Practices
Ethical approval was obtained from the biomedical research ethical committee of the University of Parakou (CLERB). The data were treated confidentially and anonymously.

Results
A total of 139 health care workers were surveyed (Fig. 1).

Socio-Demographic Characteristics of Participants
Participants mean age was 40.48±9.12 years and the sex ratio were 0.51. Nurses represented 46.76% followed by nursing auxiliary (17.27%). In terms of the hospital department, 40 (28.78%) participants worked in internal medicine and 28 (20.14%) in surgery. Table 2 presents participants general characteristics.

History of COVID-19
Of the 139 participants, 104 (74.82%) had been contacts of confirmed COVID-19 cases in the hospital setting and 18 (12.95%) had family exposure. Thirty-one participants (22.30%) had experienced a confirmed COVID-19. Of these, 29 (93.55%) had had the disease more than 6 months before the day of the survey. More than two thirds (80.65%) of the participants with confirmed COVID-19 reported having had the disease before vaccination. Four participants (12.90%) had COVID-19 after their vaccination. Table 3 presents participants exposure and history of COVID-19 data.

SARS-CoV-2 Vaccination Coverage Among Participants
One hundred and thirty-five participants (97.12%) had received at least one dose of vaccine, for an overall vaccination coverage rate of 97.12%. Of these, 49 or 36% had incomplete vaccination status. Vaccination took place more than six months before the survey in 131 (97.04%) participants. Vaccination was carried out by HCWs as a result of mandatory vaccination in 73% of cases and voluntary in 26% of cases. Table 4 presents participants vaccination data.

SARS-CoV-2 Antibodies Seroprevalence
The serological test was positive in 128 participants, for SARS-CoV-2 antibodies seroprevalence of 92.02%. According to vaccination status, the SARS-CoV-2 antibodies seroprevalence was 91.85% in vaccinated participants and 100% in unvaccinated participants. Figure 2 shows the participants SARS-CoV-2 serological profile.

Predictors of SARS-CoV-2 Seropositivity
In bivariate analysis, the associated factors of SARS-CoV-2 seropositivity were female gender (p = 0.035), use of Sinovac vaccine (p = 0.05) and completeness of vaccination status (p = 0.05). Age, occupation and location were not statistically significantly associated with the presence of antibodies (Table 5).

SARS-CoV-2 Vaccination Coverage Among Participants
Of the 139 participants, 135 had received at least one dose of one of the available COVID-19 vaccines in Benin, for an overall vaccination coverage rate of 97.12%. Vaccination coverage of HCWs varies from one setting to another depending on the vaccination policies adopted. In a systematic review of the literature, the average vaccination coverage of HCWs was 48% in West Africa (Ackah et al., 2022). According to CDC Atlanta, 68.2% of HCWs had received at least one dose of COVID-19 vaccine (Razzaghi et al., 2022). In Tunisia, coverage ranged from 55.2 (Omrane et al., 2022) to 83.5% (Snène et al., 2022) among HCWs.
The very high rate obtained in Benin is the result of compliance with the vaccination obligation imposed on this target. SARS-CoV-2 antibodies seroprevalence among health care workers.
The seroprevalence of SARS-CoV-2 antibodies among the participants at DTH-Borgou was 92.02%. This result, which can be attributed to the high vaccination coverage, raises several questions. Only 63.7% of the participants had been fully vaccinated. The most commonly used vaccines were Sinovac, the Chinese vaccine and Johnson and Johnson. This means that the 36.3% who were partially vaccinated had in fact received only one dose of the Chinese vaccine called Sinovac. In addition, no booster vaccination was performed in Benin, contrary to what is observed in developed countries (Bert et al., 2022;Edwards and Orenstein, 2022). Moreover, this seroprevalence survey was conducted more than six months after the last dose of vaccine in 97.04% of the participants. All these elements suggest that the high rate of seropositivity observed among participants cannot be the exclusive consequence of good vaccine coverage. A strong and constant exposure to the virus would certainly have contributed to maintain an immunity of the participants towards SARS-CoV-2. The proof is that 100% of the non-vaccinated participants have a positive serology.
In all cases, these results show that HCWs of all categories were mainly exposed to this virus, being in the front line of the response to COVID-19. This justifies the importance of policies aimed at reinforcing the safety of health care workers through vaccination and the strengthening of infection prevention and control measures in the health care setting.

Associated Factors of SARS-CoV-2 Seropositivity
The independent associated factors of SARS-CoV-2 seropositivity in participants surveyed in Parakou were vaccine completion and female gender. Female subjects were 10 times more likely to be seropositive than male subjects (Ora = 10.62 [2.18-51.64]). The same trend was noted in a Korean study (Choi et al., 2022) as well as in a general population seroprevalence study conducted by public health agency in France (Aumaître et al., 2022). This gender difference was also found in the Epicov study in France (Warszawski et al., 2020). It could be explained by the fact that women would be more exposed to SARS-CoV-2 as demonstrated by a study on the inequalities between men and women in relation to COVID-19 conducted in France (Neufcourt et al., 2021). The role played by women in the community, which is to take care of children, the elderly, the sick and to go to the market, for example, could explain their high exposure to the virus.
As for the completeness of the SARS-CoV-2 vaccination status, it shows that it increases the chance of having a positive serology by more than 9 times (RCa = 9.51 [1.95-46.35]) than in personnel with an incomplete vaccination status. Our observations corroborate those of other authors. Indeed, in a study in Germany, HCWs had obtained a 100% humoral response after two doses of Pfizer vaccine (Herzberg et al., 2022). These results support the use of vaccines to combat the COVID-19 pandemic. In the present study, a personal history of SARS-CoV-2 infection was associated with SARS-CoV-2 antibodies positivity. Indeed, in 100% of the cases, participants with a personal history of COVID-19 had positive serology of SARS-CoV-2. On the other hand, service was not associated with the presence of SARS-CoV-2 antibodies (p = 0.32). This was also found in the Malian study (Somboro et al., 2022). This could be due to the fact that these centers, like ours, were not exclusively dedicated to the management of patients with COVID-19. In fact, a triage system was set up in the emergency room of the DTH-Borgou, allowing patients who tested positive for SARS-CoV-2 to be referred to the epidemic management center located outside the hospital. We looked for, but did not find, an association between family and/or occupational exposure to a COVID-19 case and SARS-CoV-2 antibodies seropositivity. In a Belgian study, contact with a COVID-19-infected service colleague was not statistically associated with seropositivity. In contrast, in the same study, household contact with a COVID-19 case was associated with antibody positivity (Steensels et al., 2020). This was similar to the study conducted by public health agency in France, which found that the presence of intrafamilial clinical cases of COVID-19 increased the risk of being seropositive for SARS-CoV-2 with an Ora = 2.5 [1.3-5.0]) (Aumaître et al., 2022).

Strengths and Limitations of the Study
This study has the merit of giving a preliminary data of the SARS-CoV-2 serological profile among Beninese health care workers. It will serve as a basis for comparison in subsequent qualitative or quantitative studies.
However, the main weakness of this study remains its qualitative nature. It does not allow us to assess the degree of effective immunity of the participants. Moreover, the early start of vaccination and its imposition on health care workers did not allow us to distinguish between the spread of the virus and vaccine protection.

Conclusion
The present study found high seroprevalence among health care workers surveyed in a hospital in northern Benin. This high seroprevalence rate reflects the combined effect of high exposure to SARS-CoV-2 and COVID-19 vaccination. Further studies, especially quantitative ones, will allow a better assessment of the existence of protective immunity of the participants to this disease.