Keywords
We read with interest Jones et al.’s report of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) seroprevalence among health-care workers (HCWs) and support staff at North Bristol NHS Trust.
1
The authors reported 9.3% seroprevalence and its variation by ethnicity, with higher rate observed among non-White including Asian (14.6%) than White (8.2%). A large geographical variation of seroprevalence among HCW has been reported: higher in North America and Europe than Asia.- Jones C.R.
- Hamilton F.W.
- Thompson A.
- Morris T.T.
- Moran E.
SARS-CoV-2 IgG seroprevalence in healthcare workers and other staff at North Bristol NHS Trust: a sociodemographic analysis.
J Infect. 2020; (S0163-4453(20)30755-6)https://doi.org/10.1016/j.jinf.2020.11.036
2
In Japan, which has relatively high number of Covid-19 cases in Asia, data are limited on the seroprevalence among HCW.3
,4
National Center for Global Health and Medicine (NCGM), due to its special role in the control of infectious diseases in Japan, has been taking a leading role in combatting Covid-19 since the early phase of its epidemic, and many NCGM staff have been involved in various missions with potential exposure to SARS-CoV-2, including health check of returnees on charter flights from Hubei, China
5
and infection control on theDiamond Princess cruise ship.6
We designed a study comprising repeated cross-sectional surveys among staff of NCGM. Here, we report the results of the first survey on July 2020 (after the first wave of epidemic in Japan), which was mainly targeted for those who had worked in Covid-19 related department or was engaged in any Covid-19 related task, or nurses of inpatient ward. Of 1579 employees invited, 1228 (77.8%) agreed to participate in the survey. Written informed consent was obtained from each participant. This study was approved by the ethics committee of NCGM.We asked participants to complete an electronic questionnaire and donate venous blood. Serum separated was measured for SARS-CoV-2 antibodies by using test systems manufactured by Abbott and Roche at in-house laboratory. We run the Abbott ArchitectⓇ instrument using the SARS-CoV-2 IgG assay, based on the chemiluminescent microparticle immunoassay to detect IgG against the SARS-CoV-2 nucleoprotein, and Roche cobasⓇ e602 analyzer using the ElecsysⓇ Anti-SARS-CoV-2 based on the electrochemiluminescence immunoassay to detect total antibodies including IgG to the SARS-CoV-2 nucleoprotein. For the sample with positive on either test, we quantified IgG with Anti-SARS-CoV-2 [anti-S1] ELISA (EUROIMMUN AG, Luebeck, Germany) and neutralizing antibody titer by using live virus (Supplement).
We defined antibody positive if either test shows positive (sensitivity priority). We calculated the proportion of those with antibody positive and its 95% confidence interval (Clopper-Pearson), and compared the seroprevalence with that of the general population survey in Tokyo,
7
which used the same assays as the current study. We also defined antibody positive if both tests are positive (specificity priority).The mean (SD) age of study participants was 36 (11) years and 71% were female. As shown in Table, major occupational categories were nurses (49%), doctor (19%), other allied health care professional (14%), and clerical and administrative staff (10%). A total of 850 participants (69%) reported having being engaged in any work associated with Covid-19; of these, 343 (40%) were engaged in work with high infection risk.
TableCharacteristics of study participants.
| No. | % | |
|---|---|---|
| Total | 1228 | 100 |
| Male sex | 353 | 28.7 |
| Age, years | ||
| <30 | 465 | 37.9 |
| 30–39 | 335 | 27.3 |
| 40–49 | 257 | 20.9 |
| ≥50 | 171 | 13.9 |
| Affiliation | ||
| Hospital | 1095 | 89.2 |
| Others | 133 | 10.8 |
| Job | ||
| Doctor | 237 | 19.3 |
| Nurse | 601 | 48.9 |
| Allied health care professional | 169 | 13.8 |
| Clerical and administrative staff | 128 | 10.4 |
| Other | 93 | 7.6 |
| Occupational risk of SARS-CoV-2 infection | ||
| Low | 408 | 33.2 |
| Middle | 478 | 38.9 |
| High | 342 | 27.9 |
| Engagement in Covid-19 related work | ||
| Screening of returnees of the charter flight from Wuhan | 135 | 11.0 |
| Infection control on the cruise ship | 55 | 4.5 |
| Covid-19 testing center, fever consultation clinic | 119 | 9.7 |
| Care facility for Covid-19 patients with mild symptom | 26 | 2.1 |
| Works done within 1 m of Covid-19 patient | 526 | 42.8 |
| Works done at 1 m or more of Covid-19 patient | 315 | 25.7 |
| SARS-CoV-2 laboratory testing | 74 | 6.0 |
| Handling SARS-CoV-2 other than testing | 122 | 9.9 |
| Cleaning, laundry, sterilization, waste disposal | 222 | 18.1 |
| Fever screening of outpatient and visitors | 126 | 10.3 |
| Others | 141 | 11.5 |
| Any of the above | 850 | 69.2 |
| Symptom indicative of Covid-19 | ||
| Common cold-like symptom lasting 4 days or longer | 153 | 12.5 |
| High fever | 53 | 4.3 |
| Severe fatigue | 98 | 8.0 |
| Dyspnea | 30 | 2.4 |
| Loss of sense of taste or smell | 10 | 0.8 |
| Close contact with Covid-19 patient | 57 | 4.6 |
| History of PCR testing for SARS-CoV-2 | 91 | 7.4 |
| History of Covid-19 | 1 | 0.1 |
1 Categorized according to the type of Covid-19 related work engaged.
2 Contact with Covid-19 patient within 1 m without personal protective equipment, having lived with Covid-19 patient, etc.
Of study participants, only two were positive on either antibody test; one on Abbott test (index: 2.24) and another on Roche test (index: 7.64), giving a seroprevalence of 0.16% (95% confidence interval: 0.02 to 0.59). The observed SARS-CoV-2 seropositivity is no greater than that of the general population survey in Tokyo on June 2020 (0.41%, recalculated according to the definition of the present study).
3
The participants with positive test result were both female nurses aged 20′s, and reported having no symptoms indicative of Covid-19, no engagement in Covid-19 related work, and no close contact with infected patient without personal protecting device. Another nurse who was previously diagnosed as Covid-19 showed negative on the present antibody tests. The two positive samples on either test were proved to be negative on both EUROIMMUN IgG quantitative test and neutralizing antibody test. If we adopt specificity priority-definition of antibody positive (positive on both tests), the seroprevalence is zero.A systematic review of seroprevalence studies suggested high risk of SARS-CoV-2 infection among HCW.
2
In contrast, we observed a very low seropositive rate in the staff of NCGM as of July 2020, which was even lower than that among the general population in Tokyo. In a tertile hospital in the US, the rate of SARS-CoV-2 infection among HCW was lower than that among the general public in the surrounding region.8
The observed low seroprevalence may reflect effective infection control in the hospital. While having accepted a large number of inpatients and being involved in various Covid-19 related work since early phase of this epidemic, NCGM have introduced comprehensive measures to protect staff against the infection. These include sufficient provision with personal protective equipment for HCW depending on their infection risk, intensive and frequent hand washing/alcohol sanitation practice, universal masking, limiting visitors, checking body temperature at hospital entrance, notification of fever from staff on daily basis, SARS-CoV-2 PCR test for staff who reported fever or close contact with infected patient and for pre-operative patients, partitioning dining table with acrylic board, and periodic advisory e-mail message to the staff, all of which might have collectively contributed to minimizing infection risk in hospital. These measures have been strengthened according to the epidemic of the time.
The staff face high infection risk in their daily life outside hospital, which is located in the central Tokyo, an epicenter. NCGM has taken measures to address this issue. For instance, the infection control department delivers an e-mail on every Friday to all the staff to raise the awareness of preventive behaviors that should be taken during the weekend. Such advisory message might have contributed to high compliance of staff with preventive practice and lowering risk of community-acquired infection.
In conclusion, this seroepidemiological study in a large hospital in Tokyo adds evidence to support that comprehensive infection control measures in hospital can decrease risk of SARS-CoV-2 infection among HCW combatting Covid-19 to the levels comparable to or even lower than that of the general population. Repeated testing of antibody among HCW is warranted to monitor the spread of infection and assess control measures in hospital.
Declaration of Competing Interest
Antibody test reagents were provided from Abbott and Roche Diagnostic to the present study.
Acknowledgement
Shinji Kobayashi, Yusuke Oshiro, Mitsuru Ozeki (Department of Laboratory Testing, Center Hospital of the National Center for the Global Health and Medicine);
Kouki Matsuda (Department of Refractory Viral Infection, Research Institute, National Center for Global Health and Medicine);
Masamichi Ishii (Center for Medical Informatics Intelligence, National Center for the Global Health and medicine);
Ryuma Hirabayashi (National Center for the Global Health and medicine);
Tomoko Nakayama (Center Hospital of the National Center for the Global Health and medicine);
Ayako Mikami, Moto Kimura, Maki Konishi (Center for Clinical Sciences, National Center for Global Health and Medicine)
Funding
This work was supported by the NCGM COVID-19 Gift Fund and the Japan Health Research Promotion Bureau Research Fund (2020-B-09).
Role of the Funder/Sponsor
The funder did not play any role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; or decision to submit the manuscript for publication.
Appendix. Supplementary materials
References
- SARS-CoV-2 IgG seroprevalence in healthcare workers and other staff at North Bristol NHS Trust: a sociodemographic analysis.J Infect. 2020; (S0163-4453(20)30755-6)https://doi.org/10.1016/j.jinf.2020.11.036
- Seroprevalence of SARS-CoV-2 antibodies and associated factors in health care workers: a systematic review and meta-analysis.J Hosp Infect. 2020; 108: 120-134
- Survey of the current status of subclinical coronavirus disease 2019 (COVID-19).J Infect Chemother. 2020; 26: 1294-1300
- SARS-CoV-2 IgG seroprevalence among medical staff in a general hospital that treated patients with COVID-19 in Japan: retrospective evaluation of nosocomial infection control.J Hosp Infect. 2021; 107: 103-104
- SARS-CoV-2 infection among returnees on charter flights to Japan from Hubei, China: a report from National Center for Global Health and Medicine.Glob Health Med. 2020; 2: 107-111
- Epidemiology and quarantine measures during COVID-19 outbreak on the cruise ship Diamond Princess docked at Yokohama, Japan in 2020: a descriptive analysis.Glob Health Med. 2020; 2: 102-106
- Results of a survey on SARS-CoV-2 antibody in the general population in Japan.June 16, 2020 (PublishedAccessed August 18, 2020) (in Japanese)
- Prevalence of SARS-CoV-2 infection among health care workers in a tertiary community hospital.JAMA Intern Med. 2020; e204214
Article info
Publication history
Published online: January 28, 2021
Accepted:
January 17,
2021
Identification
Copyright
© 2021 The British Infection Association. Published by Elsevier Ltd. All rights reserved.
