puts a heavy burden not only on patients' physical and mental health but also on regional health care resource and economic activity across the world. To judge the policy decision and overcome this pandemic, we should collect fundamental epidemiological information as soon as possible. The standard diagnosis of COVID-19 is based on viral nucleic acid detection using reverse-transcription polymerase chain reaction (RT-PCR) assay of SARS-CoV-2. Whereas RT-PCR assay can detect active COVID-19 case with high accuracy, it is difficult to identify whether subjects have prior SARS-CoV-2 infection or not. Compared to RT-PCR assay, the detection of antibody can provide the . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted May 19, 2020. . https://doi.org/10.1101/2020.05.12.20098962 doi: medRxiv preprint 7 otolaryngologist and emergency physicians. We prospectively recruited medical doctors, nurses and ward clerks from our hospital between April 10 and April 20, 2020. All participants were asymptomatic and belonging to any of following sections; the department of infectious disease, respiratory medicine ward, otolaryngology ward and emergency medicine ward. We selected health-care workers from these wards because staffs belonging to these wards were more likely to contact suspected COVID-19 patients whether or not they were aware. We also retrieved the questionnaires as following items; history of seasonal common cold from winter 2019 to early spring 2020 and history of regular contact with children under 12 years old. These questionnaires were set based on the investigation of behavior pattern refer to the previous study of H10N8 avian influenza virus.(5)
We collected 6ml whole blood from each participant between April 10 and April 20, 2020. After extracting serum, we stocked them at -80 deep freezer. We evaluated the serum IgG antibody against SARS-CoV-2 by enzyme-linked immunosorbent (ELISA) assay test using novel coronavirus COVID-19 IgG ELISA kits (DRG international, Inc. Springfield, NJ, USA) according to instruction . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The optical density of each well was determined by a microplate reader set to 450 nm within 10 minutes. For detection of IgG, the cut off value was modified by using inner negative control. We interpreted the results as positive, borderline and negative in accordance with instruction manual.
Data were analyzed using JMP version 14.0.0 (SAS institute Inc. Cary, NC). The Fisher's exact test was used to compare proportions among IgG SARS-CoV-2 antibody status. Wilcoxon rank sum tests or Kruskal-Wallis tests where appropriate were used to compare the titer of SARS-CoV-2 IgG antibody between groups. A P value of less than 0.05 was considered statistically significant.
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This study was approved by the institutional review boards (approved number 20-009). We obtained written consent form of this study from all participants.
We recruited 92 health-care workers in our hospital. Medical doctors, nurses and medical clerks were 42 (45.7%), 48 (52.2%) and 2 (2.2%), respectively. Table 1 showed characteristics of participants. Of 92 participants, 59 (64.1%) were female and most prevalent age-group was twenties and thirties.
Otolaryngology ward was the most frequent working place followed by respiratory medicine ward and emergency medicine ward. There were 47 (51.1%) participants had clear history of seasonal common cold symptoms from winter 2019 to early spring 2020. There were 19 (20.7%) participants had history of regular contact with children under 12 years old.
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A total 92 serum samples collected between April 10 and April 20, 2020 were tested for ELISA designed for detecting IgG antibody against SARS-CoV-2. Of 92 participants, 5 (%), 15 (16.3%) and 72 (78.3%) showed positive, borderline and negative results of SARS-CoV-2 IgG antibody, respectively (Table 1) . Table 2 showed antibody status by occupations. There were no significant differences in the status of positive and borderline SARS-CoV-2 IgG antibody between medical doctor group and nurse and medical clerk group. Table 3 showed antibody status by wards. Two and 3 participants with positive antibody were detected in respiratory disease ward and otolaryngology ward, respectively. The highest prevalent ward where participants with positive and borderline SARS-CoV-2 IgG antibody working was otolaryngology ward. On the contrary, the lowest prevalent ward was emergency medicine ward. Table 4 showed antibody status by the response to questionnaire and history of opportunity of viral infection. Participants with a history of seasonal common cold from winter 2019 to early spring 2020 significantly showed high rate of positive SARS-CoV-2 IgG antibody than participants without those history (p=0.046). There were no significant differences in prevalence of positive SARS-CoV-2 IgG . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted May 19, 2020. . antibody between participants with a history of regular contact with children and history of opportunity of viral infection. 
In this study, we found 5 (5.4%) and 15 (16.3%) of health-care workers in our hospital showed positive and borderline results of SARS-CoV-2 IgG antibody. Mean titer of antibody of borderline results group was sharply distinguished from negative results group. These participants with borderline antibody results were suggested to be latently sensitized by patients with COVID-19.
Because our hospital officially accepted the patients with diagnosed COVID-19 since April 15, 2020, the antibody status of participants would reflect community acquired or unconscious exposure in daily medical practice.
We found that mean titer of antibody was significantly higher in otolaryngology ward than in other wards. This suggested that health-care workers belonging to otolaryngology ward were more likely to expose SARS-CoV-2.
According to the official statements of Kyoto city, confirmed incidence and case fatality of COVID-19 in Kyoto city at the end of April, were 215 cases and 11 deaths, respectively.(6) It is . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted May 19, 2020. . https://doi.org/10.1101/2020.05.12.20098962 doi: medRxiv preprint interesting that prevalence of participants with positive antibody of our study are much higher than the prevalence expected from situation reports of the government. Furthermore, number of participants with borderline antibody of our study were about 3-fold higher than those with positive antibody.
Recently several studies also revealed that seroprevalence of SARS-CoV-2 in sample population showed higher than confirmed cases. . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted May 19, 2020. . https://doi.org/10.1101/2020.05.12.20098962 doi: medRxiv preprint According to the epidemiological data provided by WHO (1) and Johns Hopkins University (4), incidence rates and case fatality rates in major European countries (Germany, UK, France, Italy and Spain) and the United States are much higher than those in major Asian countries (China, Japan, South Korea and Taiwan). There are apparent discrepancies in case fatality between Western countries and Asian countries. This phenomenon has raised some speculations. Differences in lifestyle and behavioral habits between Western and Asian countries may affect to a certain degree.
and mortality for COVID-19.(10, 11) Although this hypothesis is interesting and at least two There are several limitations in this study. First, because this study was conducted only in a single medical center, selection bias is not ignored. Second, small sample size made a statistical power vulnerable. Third, because we recruited the participants from the wards where health-care workers were more likely to contact with patients suspected of COVID-19, our results would be overestimated as compared to general health-care workers and general population. Fourth, because COVID-19 pandemic is an ongoing emerging situation, there are many premature studies published.
We occasionally have to discuss based on these premature studies.
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In conclusion, we showed relatively high prevalence of positive and borderline SARS-CoV-2 antibody in health-care workers in the southern part of Kyoto city, where located in World-Heritage area and fulfilled with inbound tourists. We suspected that COVID-19 had already spread at early stage of pandemic in Kyoto in accordance with results from our study. Although there have been published several studies evaluating profiles of SARS-CoV-2 antibody in patients with COVID-19,(15-17) our study is the first study quantitatively evaluating the antibody in health-care workers during the COVID-19 peri-pandemic period. Serial evaluation of SARS-CoV-2 IgG antibody will reveal more detailed risk factors and ways of spread of COVID-19.
Finally, we should keep in mind there is still no evidence that people who have developed antibodies after recovering from COVID-19 are protected against a second infection.
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The copyright holder for this preprint this version posted May 19, 2020. . . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted May 19, 2020. . Data are shown as number (%).
Abbreviation: SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2 *We asked history of seasonal common cold symptoms from winter 2019 to early spring 2020 and history of regular contact with children under 12 years old.
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The copyright holder for this preprint this version posted May 19, 2020. . **We defined the participants having opportunity of viral infection as having history of seasonal common cold symptoms and/or examining patients with common cold in outpatients clinics.
. CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted May 19, 2020. is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint Data are shown as number (%). A P value was estimated by using the Fisher's exact test. A P value of less than 0.05 was statistically significant.
Abbreviation: SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2 *We asked history of seasonal common cold symptoms from winter 2019 to early spring 2020, of regular contact with children under 12 years old, and of opportunity of viral infection. **We defined the participants having opportunity of viral infection as having history of seasonal common cold symptoms and/or examining patients with common cold in outpatient's clinics.
.
It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)
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