The authors have declared that no competing interests exist.
COVID-19 is a global threat with an increasing number of infections. Research on IgG seroprevalence among health care workers (HCWs) is needed to re-evaluate health policies. This study was performed in three pandemic hospitals in Istanbul and Kocaeli. Different clusters of HCWs were screened for SARS-CoV-2 infection. Seropositivity rate among participants was evaluated by chemiluminescent microparticle immunoassay. We recruited 813 non-infected and 119 PCR-confirmed infected HCWs. Of the previously undiagnosed HCWs, 22 (2.7%) were seropositive. Seropositivity rates were highest for cleaning staff (6%), physicians (4%), nurses (2.2%) and radiology technicians (1%). Non-pandemic clinic (6.4%) and ICU (4.3%) had the highest prevalence. HCWs in “high risk” group had similar seropositivity rate with “no risk” group (2.9 vs 3.5
In late 2019, a novel coronavirus (SARS-CoV-2) has emerged in Wuhan, China and posed a global threat to public health with a quick spread and escalating mortality. As of June, 2020, SARS-CoV-2 related disease COVID-19 affected more than nine million people worldwide, and caused more than one million deaths [
Typical initial clinical signs of COVID-19 have been reported as fever, dry cough, fatigue, headache and shortness of breath [
Based on genome sequence analysis, SARS-CoV-2 genome was reported to contain 14 Open Reading Frames (ORFs) encoding 27 proteins [
Istanbul is the epicenter of the ongoing pandemic in Turkey and 60% of the confirmed cases are from Istanbul [
This study was conducted in three pandemic hospitals in Istanbul and Kocaeli, including University of Health Sciences Umraniye Teaching and Research Hospital (UEAH), Istanbul University-Cerrahpasa, Cerrahpasa Medical Faculty Hospital (Cerrahpasa), Darica Farabi Teaching and Research Hospital (Farabi). HCWs were invited to participate in the study. Exposure risk of the HCWs was determined by the working areas they were assigned during the pandemic. Some HCWs were on administrative leave due to their medical conditions and they were classified as having “no risk”. HCWs working in the clinics, which were kept clear of COVID-19 or had no direct contact with any patient, were classified as having “low risk”. HCWs employed in hot zones for COVID-19 transmission including emergency unit, intensive care unit (ICU), pandemic clinics, COVID outpatient clinics, COVID testing labs, departments of Infectious Diseases and Chest Medicine, and radiology department (where CT scans and chest X-rays were performed) were classified as having “high risk”. HCWs with administrative roles for supervising hot zones with regular visits were also classified in the “high risk” group. We also recruited HCWs who were diagnosed with COVID-19 at least 14 days before enrollment for the study. This group was defined as the “PCR positive” group. Demographics data, comorbidities, drug history, date of COVID-19 diagnosis, past PCR tests, results of chest computed tomography (CT) scans were noted. HCWs not willing to give consent, HCWs with a history of COVID-19 diagnosis without a confirmatory PCR test and those diagnosed within the last 14 days were excluded. All blood samples were collected in the three hospitals in between 30th May and 6th of June 2020. Oro-nasopharyngeal swab samples of the three subgroups (excluding PCR positive group) were also tested to confirm the absence of active infection at the time when blood specimens were collected.
All sera samples were aliquoted after centrifugation of peripheral blood tubes at 800xg for 12 minutes and sera samples were kept in -20°C until the study day. For detection of SARS-CoV-2 IgG, chemiluminescent microparticle immunoassay (Abbott Laboratories, Cat no: 6R86, Lot no: 16253FN00) was carried out according to manufacturer’s instructions and samples were run on the related instrument (ARCHITECT, Abbott Laboratories, Abbott Park, IL, USA). Minimum 100 μL of serum was required for analysis. Qualitative results were reported by the instrument with the cut-off value of 1.40 S/C as recommended. This study was approved by the ethics committee of the Umraniye Teaching and Research Hospital (approval number: 29.05.2020/10337). Written informed consent was obtained from each enrolled participant. All study was carried out in accordance with the ethical standards of the Helsinki Declaration.
All statistical analyses were performed by SPSS version 22 software (Chicago, IL). Parametric variables were analyzed by Student’s
In the end of May, Ministry of Health Department declared that the seropositivity in population was 0.8% in Turkey and there was no seroprevalence study for HCWs until June 2020. Also, in another study, seropositivity was 8% for HCWs in Spain [
The timeline showing the progression of COVID-19 pandemic in Turkey, which includes events from the date that the country’s first coronavirus case has been announced, was given in
Hospitals | ||||
---|---|---|---|---|
UEAH | Cerrahpasa | Farabi | Total | |
836 | 880 | 350 | 2066 | |
410 | 222 | 300 | 932 | |
2528 | 1056 | 1853 | 5437 | |
14906 | 21970 | 12375 | 49251 | |
3232 | 3723 | 1373 | 8328 | |
|
125 (3.8%) | 107 (2.8%) | 14 (1%) | 241 (2.8%) |
|
105 (3.2%) | 84 (2.2%) | 8 (0.5%) | 187 (2.2%) |
1 | 0 | 0 | 1 | |
0 | 0 | 0 | 0 |
All data is given for the period between 1 March and 30 May 2020. HCW: Health Care Worker.
Health Care Workers | |||||
---|---|---|---|---|---|
Characteristics | No Risk n = 113 (%) | Low Risk n = 157 (%) | High Risk n = 543 (%) | PCR Positive n = 119 (%) | Total n = 932 (%) |
UEAH | 52 (46.0) | 0 | 218 (40.1) | 52 (43.7) | 322 (34.5) |
Cerrahpasa | 58 (51.3) | 54 (34.4) | 124 (22.8) | 64 (53.8) | 300 (32.2) |
Farabi | 3 (2.7) | 103 (65.6) | 201 (37.0) | 3 (2.5) | 310 (33.3) |
34.5± 12.23 | 35.5± 8.86 | 34.3± 8.92 | 36.2± 10.14 | 34.8± 9.54 | |
Male | 56 (49.6) | 53 (33.8) | 184 (33.9) | 39 (32.8) | 332 (35.6) |
Female | 57 (50.4) | 104 (66.2) | 359 (66.1) | 80 (67.2) | 600 (64.4) |
Physician | 62 (54.9) | 12 (7.6) | 175 (32.2) | 30 (25.2) | 279 (29.9) |
Nurse | 17 (15.0) | 32 (20.4) | 174 (32.0) | 45 (37.8) | 268 (28.8) |
Ward Clerk&Security | 12 (10.6) | 67 (42.7) | 35 (6.4) | 15 (12.6) | 129 (13.8) |
Lab&Radiology Technician | 1 (0.9) | 7 (4.5) | 92 (16.9) | 7 (5.9) | 107 (11.5) |
Cleaning Staff | 12 (10.6) | 10 (6.4) | 62 (11.4) | 12 (10.1) | 96 (10.3) |
Administrative Staff | 9 (8.0) | 29 (18.5) | 5 (0.9) | 10 (8.4) | 53 (5.7) |
Pandemic Clinic | 0 | 0 | 284 (52.3) | 51 (42.8) | 335 (35.9) |
Intensive Care Unit | 0 | 0 | 69 (12.7) | 10 (8.4) | 79 (8.5) |
Emergency Room | 0 | 0 | 47 (8.7) | 8 (6.7) | 55 (5.9) |
Corona Lab | 0 | 0 | 61 (11.2) | 1 (0.8) | 62 (6.7) |
Swab Team | 0 | 0 | 51 (9.4) | 4 (3.4) | 55 (5.9) |
Non-Pandemic Clinic | 0 | 50 (31.9) | 28 (5.1) | 30 (25.2) | 108 (11.6) |
Administrative Office | 0 | 107 (68.2) | 3 (0.6) | 15 (12.6) | 125 (13.4) |
On leave | 113 (100) | 0 | 0 | 0 | 113 (12.1) |
Chronic Disease Present | 31 (27.4) | 19 (12.1) | 61 (11.2) | 31 (26.1) | 142 (15.2) |
Hypertension | 8 (7.1) | 7 (4.5) | 19 (3.5) | 7 (5.9) | 41 (4.4) |
Diabetes Mellitus | 5 (4.4) | 2 (1.3) | 16 (2.9) | 6 (5.0) | 29 (3.1) |
Other Chronic Disease | 22 (19.5) | 11 (7.0) | 29 (5.3) | 19 (16.0) | 81 (8.7) |
ACE inh./ARB | 6 (5.3) | 5 (3.2) | 16 (2.9) | 8 (6.7) | 35 (3.8) |
Immuno-suppressive drug | 2 (1.8) | 1 (0.6) | 2 (0.4) | 2 (1.7) | 7 (0.8) |
Smoking | 25 (22.1) | 42 (26.8) | 147 (27.1) | 14 (11.8) | 228 (24.5) |
4 (3.5) | 2 (1.3) | 16 (2.9) | 93 (78.2) | 115 (12.3) | |
Symptoms | n.a. | n.a. | n.a. | 98 (82.4) | 98 (10.5) |
CT Result | n.a. | n.a. | n.a. | 71 (59.7) | 71 (7.6) |
ACE inh.: Angiotensin-converting enzyme (ACE) inhibitor, ARB: Angiotensin II receptor blocker, CT: Computed tomography scan, HCW: Health Care Worker, n.a: Not applicable.
IgG antibodies against SARS-CoV-2 in serum samples of all participants were detected by chemiluminescent microparticle immunoassay. The rate of seroprevalence was 2.7% among non-infected HCWs (
Characteristic | No Risk n = 113 (%) | Low Risk n = 157 (%) | High Risk n = 543 (%) | Total n = 813 (%) |
---|---|---|---|---|
4 (3.5) | 2 (1.3) | 16(2.9) | 22 (2.7) | |
UEAH | 1 (1.9) | N/A | 3 (1.3) | 4 (1.5) |
Cerrahpasa | 3 (5.1) | 2 (3.7) | 12 (9.6) | 17 (7.2) |
Farabi | 0 | 0 | 1 (0.4) | 1 (0.3) |
0.4 ±0.18 | 0.3 ±0.11 | 0.1 ±0.16 | 0.3 ±0.16 |
N/A: Not Available.
Characteristic n (%) | IgG Negative n = 791 | IgG Positive n = 22 | OR | 95% CI | |
---|---|---|---|---|---|
Physician | 239 (96.0) | 10 (4.0) | 1.93 | 0.82–4.51 | 0.16 |
Nurse | 218 (97.7) | 5 (2.2) | 0.77 | 0.28–2.12 | 0.81 |
Ward Clerk&Security | 113 (99.1) | 1 (0.9) | 0.29 | 0.04–2.15 | 0.35 |
Lab&Radiology Technician | 99 (99.0) | 1 (1.0) | 0.33 | 0.04–2.50 | 0.51 |
Cleaning Staff | 79 (94.0) | 5 (6.0) | 2.65 | 0.95–7.38 | 0.07 |
Administrative Staff | 43 (100) | 0 | n.a. | n.a. | 0.62 |
Pandemic Clinic | 276 (96.8) | 9 (3.2) | 1.3 | 0.55–3.08 | 0.65 |
Intensive Care Unit | 66 (95.6) | 3 (4.3) | 1.73 | 0.5–6.01 | 0.42 |
Emergency Room | 46 (97.9) | 1 (2.1) | 0.77 | 0.10–5.86 | 1.00 |
Corona Lab | 61 (100) | 0 | n.a. | n.a. | 0.4 |
Swab Team | 51 (100) | 0 | n.a. | n.a. | 0.63 |
Non-Pandemic Clinic | 73 (93.6) | 5 (6.4) | 2.89 | 1.04–8.61 | 0.05 |
Administration Office | 111 (100) | 0 | n.a. | n.a. | 0.06 |
On leave | 107 (96.4) | 4 (3.6) | 1.39 | 0.46–4.19 | 0.53 |
n.a: Not applicable, OR: Odd Ratio, CI: Confidence Interval.
To assess antibody production in COVID-19 patients, we analyzed the positive rates of IgGs in sera of all HCWs after 52.8±11.6 days post-infection. IgGs for SARS-CoV-2 were detected in 78.2% of convalescent COVID-19 patients (
Health care systems are under tremendous pressure due to the lack of curative treatment for COVID-19 [
HCWs employed in coronavirus testing labs (Corona lab) and swab teams were reasonably anticipated to be at high risk. In this study, we did not observe seropositivity in these personnel, they were found to be efficiently protected from the disease. Although the seropositivity was statistically higher in non-pandemic clinics, factors including public transportation, poor housing conditions, limited personal space and thus reduced compliance with social distancing, which are not addressed in this study, must be considered to analyze the transmission of disease among HCWs. All staff in hospitals should be well-trained on elements of disease transmission; such as the sources of exposure to the virus, risks associated with the exposure and suitable occupational protocols. Such data implied that the risk of viral transmission in these areas are widely underestimated and utmost caution is urged in all zones of the hospitals.
Limited data are available for asymptomatic or subclinical infections in transmission of SARS-CoV-2 virus [
Although overall seropositivity among HCWs was calculated as 2.7% in our study, fluctuations between institutions were also noted. A lower rate at Farabi (0.3%) might be presumable, as PCR confirmed HCW rate was also not that high (0.5%). On the other hand, between two institutions with comparable PCR confirmed HCW rates, observed seropositivity of HCWs from Cerrahpasa was found to be significantly higher than those from UEAH (7.2% and 1.5% respectively). As we compared the work schedules of HCWs in three hospitals, we noticed that physicians in Cerrahpasa was assigned to the pandemic clinics on daily basis. On the other days of the week the same physician served at non-pandemic clinic, too. The work schedule was made on monthly basis in UEAH and Farabi. Moreover, at Cerrahpasa as being a distinguished medical school, teaching on ward rounds with medical students resumed until 18th of March. UEAH and Farabi do not teach undergraduate students. Cerrahpasa’s buildings were being reconstructed when the outbreak began in Turkey and this might have also impaired some infection control measures.
The information for SARS-CoV-2 transmission among health care workers could help for the revision of health policies and immunization strategies in hospitals for a possible resurgence of the outbreak. Further, extensive knowledge of antibody seroconversion and characterization of antibody profiles throughout SARS-CoV-2 infection could provide insights for the identification of potentially targeted neutralizing antibodies.
Even though a significant number of employees were tested, not all of the invited HCWs in these hospitals participated in the study. Screening larger cohorts from hospitals could serve more information to monitor the course of pandemic among HCWs. Furthermore, a group of HCWs might have be reported as negative just because of the tendency of IgG titers to drop time-dependently.
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We appreciate the generous contribution of Abbott for providing Architect SARS-CoV-2 IgG antibody kits, the chemiluminescence microparticle immunoassay method, to our institutions. We thank Yesim Karaca, Aleyna Karaca, İrem Yaren Nur and Murat Kaya for technical assistance.