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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 12  |  Issue : 2  |  Page : 51-57

Antibody response to SARS-CoV-2-infected healthcare workers during first wave of Covid-19 pandemic in a tertiary care center of Assam


1 Department of Pathology, Lakhimpur Medical College and Hospital, Lakhimpur, India
2 Department of Microbiology, Assam Medical College and Hospital, Dibrugarh, Assam, India
3 Department of Microbiology and Nodal Officer, Multidisciplinary Research Unit, Assam Medical College and Hospital, Dibrugarh, Assam, India
4 Department of Pathology, Assam Medical College and Hospital, Dibrugarh, Assam, India
5 Department of Biochemistry, Assam Medical College and Hospital, Dibrugarh, Assam, India
6 Department of Multidisciplinary Research Unit, Assam Medical College and Hospital, Dibrugarh, Assam, India

Date of Submission07-Jul-2022
Date of Acceptance16-Aug-2022
Date of Web Publication23-Nov-2022

Correspondence Address:
Gayatri Gogoi
Department of Pathology, Lakhimpur Medical College and Hospital, Lakhimpur, Assam
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ajoim.ajoim_10_22

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  Abstract 

Context: Healthcare workers (HCWs) were at the front line of the COVID-19 (corona virus disease-19) pandemic management and were at higher risks of contracting SARS-CoV-2 due to occupational exposure. The objectives of the present study were to estimate the antibody response to SARS-CoV-2 among COVID-19-positive HCWs and its persistence in subsequent follow-up samples and to compare antibody response between rapid antigen/real time polymerase chain reaction (RT-PCR) groups. Settings and Designs: This hospital-based cross-sectional study was carried out in Assam Medical College. Materials and Methods: Inclusion criteria were SARS-CoV-2 test, which was confirmed in HCWs. A total of 127 HCWs were included. The samples were tested for SARS-CoV-2 IgG by qualitative indirect ELISA using InBios SCoV-2 DetectTM IgG kit. First sample was collected from 25th day to 35th day of SARS-CoV-2. First and second follow-up samples were collected in 3 and 6 months, respectively. Statistical Analysis Used: Epi Info version 7 was used. The χ2 test was done. Results: A total of 69% male and 31% female HCWs were included. Most of them were in the 20–29 years age group (48%). About 92% were symptomatic and 20% had comorbidities. Overall seroconversion was 88% (RAT category 98.61% and RT-PCR 74.55%). Symptomatic category showed 90.68% seropositivity. The follow-up at the 3rd and 6th month showed 93.85% and 88.24% seropositivity, respectively. Conclusion: Rapid antigen test-positive symptomatic people have more chances of development of antibodies within a period of 1 month and sustained for more than 6 months in their blood.

Keywords: Healthcare workers, rapid antigen tests, RT-PCR, SARS-CoV-2 antibodies, symptomatic


How to cite this article:
Gogoi G, Medhi M, Nath R, Dutta U, Borgohain M, Gohain B, Bhattacharyya N, Hussain ME. Antibody response to SARS-CoV-2-infected healthcare workers during first wave of Covid-19 pandemic in a tertiary care center of Assam. Assam J Intern Med 2022;12:51-7

How to cite this URL:
Gogoi G, Medhi M, Nath R, Dutta U, Borgohain M, Gohain B, Bhattacharyya N, Hussain ME. Antibody response to SARS-CoV-2-infected healthcare workers during first wave of Covid-19 pandemic in a tertiary care center of Assam. Assam J Intern Med [serial online] 2022 [cited 2022 Nov 29];12:51-7. Available from: http://www.ajimedicine.com/text.asp?2022/12/2/51/361822


  Introduction Top


Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and coronavirus disease 2019 (COVID-19) emerged from Wuhan, Hubei Province, China in December 2019, and the World Health Organization (WHO) declared a pandemic situation on 11th March 2020.[1] As of March 9, 2022, the WHO reported 448,313,293 confirmed cases and 6,011,482 deaths globally due to COVID-19. In India from January 3, 2020 to March 9, 2022, there have been 42,975,883 confirmed cases with 515,355 deaths.[2]

Healthcare workers (HCWs) were at the front line of the coronavirus disease management and proportionally were at higher risks of contracting SARS-CoV-2 due to occupational exposure to droplets, aerosols, and contaminated surfaces.[3] The detection of SARS-CoV-2 was used to be done by highly sensitive real time polymerase chain reaction (RT-PCR).[4] Rapid antigen tests (RAT) were on extensive use in clinical setting for screening of positive cases to save time and expedite management.[5]

India was the one of the countries most affected by recent COVID-19 pandemic and Assam was the most affected state in the North East with around 152,000 COVID-19 positive cases in total as on September 20, 2020. One of the most affected subsets of population was HCWs, due to repeated professional exposure in their duties. All the tertiary care centers in Assam were the Designated COVID hospitals in which COVID and non-COVID care was provided in parallel manner.

Some of the initial studies threw light on the development of IgG antibodies in convalescent period starting from 2 to 3 weeks, which was detected by conversion antibody detection methods and continue to remain till 3 months’ time.[6] One UK-based study showed that 44% of HCWs had evidence of SARS-CoV-2 infection either by RT-PCR or serology, which was higher than the community in the UK and worldwide.[7]

The development of immunity to natural infection is both cellular and humoral type.[8] The first response is non-specific then followed by an adaptive response where the body makes antibodies that specifically bind to the virus such as SARS CoV2. B lymphocytes produce antibodies that are specific to that virus. IgM antibodies can be detected as early as 3 days after infection and act as first line of defence. After which high-affinity IgG responses lead to long-term immune memory. A study by Hao et al. reported that in COVID19 patients, IgM antibodies were generated 1 week after the onset of symptoms and reached its peak in 2–3 weeks. Meanwhile, IgG levels increased quickly beginning a little later compared with IgM and were maintained at a high level for 2 months. Therefore, the detectable levels of IgM and IgG antibodies could provide information regarding serological conversion over the disease course, as the detection of IgM antibody indicates a recent exposure to SARS-CoV-2 and the detection of IgG antibody in the absence of detectable IgM antibody indicates prior virus exposure.[9]

Based on the above concept, convalescent plasma therapy was being used in Assam, India, for the treatment of Covid patients. When we theoretically conceptualized that, more symptoms or more viral load should elicit higher immune response hence probably higher antibody titer but unable to establish it without taking up a systematic study. So our aim was to understand whether repeated exposure would generate more antibodies without clinical symptoms or symptomatic people had more chances to develop antibodies. The aim of this article is to compare the development of antibodies depending on CT value of RT-PCR and positivity etc.

Objectives

  • To estimate the antibody response to SARS-CoV-2 virus infection among the study participants (HCWs);


  • To estimate persistence of SARS-COV-2 antibody in subsequent follow-up samples at 3 and 6 months;


  • To compare SARS-CoV-2 antibody response between two viral detection tests: RAT/RT-PCR.



  •   Materials and Methods Top


    This hospital-based cross-sectional study was carried out in the Multidisciplinary Research Unit (MRU), ICMR, Basic Science Building, Assam Medical College. The study period was from February 4, 2020 to February 3, 2021.

    HCWs who were engaged in the patient care, either directly as doctors and nurses or indirectly as assistants, technicians, and other support staff (e.g., administrative staff, cleaner, etc.), employed under the institution were part of this study.



    Inclusion criteria

    This includes SARS-CoV-2-positive HCWs either by RT-PCR or by RAT test who were above 18 years of age and both genders working in different departments of Assam Medical College and hospital.

    Exclusion criteria

    1. Symptomatic HCWs but not positive by RT-PCR or RAT


    2. Those not willing to give consent for the study.


    3. Positive for more than 2 months.


    Tests used for SARS-CoV-2 detection

    1. Rapid antigen test kit: Detection of SARS-CoV-2 was done by standard Q COVID-19 Ag, SD Biosensor, South Korea/India.


    2. RT-PCR kit: The following kit was used: multiplex RT-PCR TaqPath™ COVID-19 RT-PCR kit from Applied Biosystems (Thermo Fisher Scientific, USA) or TRUPCR®SARS-CoV-2 RT-qPCR kit, Kilpest India Limited, whichever was available in the laboratory during the investigation time period.


    Ethical approval for the study was obtained from the Institutional Ethics Committee (Human).

    Sampling method and data collection

    Convenient sampling method was used and all the participants were approached telephonically. A total of 127 participants were enrolled. Written and informed consent was obtained from the study subjects prior to the enrolment. A predesigned proforma was used for the collection of following information from each participant: demographics (age, sex, etc.), professional information (occupation, department, etc.), clinical information (cough, sore throat, chest pain, nasal discharge, fatigue, shortness of breath, fever, headache, abdominal pain, nausea, vomiting, hemoptysis, diarrhea, body ache, loss of smell, chills, etc.), history of COVID 19 test—RT-PCR/RAT, and comorbidities.

    Sample collection and storage

    An aliquot of 3 mL of venous blood was collected using a standard venipuncture technique or a clot activator vial by maintaining universal precaution. The samples were kept at room temperature for half an hour and then centrifuged to get the serum. The serum samples were stored at 4°C in a refrigerator for 48 h and -80°C for long-term preservation.

    Sample processing

    After thawing the samples, they were tested for SARS-CoV-2 IgG by qualitative indirect ELISA method using InBios SCoV-2 DetectTM IgG ELISA Kit (InBios International Inc., Seattle, WA, USA), following manufacturer’s instruction.

    Principles

    The SCoV-2 Detect™ IgG ELISA is a qualitative indirect ELISA for the detection of IgG antibodies targeting epitopes derived from SARS-CoV-2. Diluted serum specimens are added to antigen-coated wells and incubated. After incubation and washing, human antibodies targeting SARS-CoV-2 antigens remain bound to the plate surface. Secondary antibody conjugated to horseradish peroxidase targeting human IgG is then added to each well. After incubation, the ELISA wells are washed once again before a tetramethylbenzidine substrate is added. An acidic stopping solution is finally used to stop the reaction, and the degree of enzymatic turnover of the substrate is determined by absorbance measurement at 450 nm.

    Follow-up

    The first sample was collected between 25th and 35th days of the SARS-CoV-2 test, and second sample or first follow-up samples were collected from the SARS-CoV-2 IgG-positive cases in 3 months followed by collection of third sample or second follow-up sample at 6 months.

    Statistical analysis

    Analysis was done using Epi Info software (version 7.1.3, Atlanta, GA, USA). A χ2 test was used to calculate and P < 0.05 was considered to be statistically significant.


      Results Top


    A total of 127 HCWs were included in the study and the serial samples were tested. The results were as discussed in [Table 1][Table 2][Table 3][Table 4][Table 5][Table 6][Table 7][Table 8][Table 9][Table 10][Table 11][Table 12][Table 13][Table 14][Table 15][Table 16][Table 17][Table 18][Table 19][Table 20][Table 21]. In the demographic profile [Table 1] majority of HCWs belonged to 20–29 years age group, male and were doctors. Clinical and medical characteristics of the study population [Table 2] showed most were (92%) symptomatic and with no comorbidity (80.31%). Fever was the most common symptom followed by body ache, cough and sore throat [Table 3]. The most common comorbid condition in the study population was hypertension followed by alcohol, smoking and diabetes [Table 4]. While comparing antibody response in the study population, 88% turned out to be antibody positive [Table 5], among which more were in 20–29 years age group [Table 6], blood group had no significant role [Table 7], had no comorbidity [Table 8], and occupation too had no significant role [Table 9]. In the first sample antibody response were higher in RAT positive cases [Table 10] and in symptomatic ones [Table 11]. In the second sample (first follow up) collected after 3 months interval 65 HCWs were enrolled and their sample analysis showed more antibody response in non-comorbid cases [Table 12], occupation played no significant part [Table 13], more in symptomatic cases [Table 14], and almost equal response in both RAT and RT-PCR positive cases [Table 15]. In the second follow up, 17 HCWs turned up for enrolling, samples were collected after 6 months and the results showed no significant correlation of antibody response with age [Table 16], blood group [Table 17], comorbidity [Table 18], occupation [Table 19], symptoms [Table 20] and RAT/RT-PCR positivity [Table 21].
    Table 1: Demographic characteristics of the study population

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    Table 2: Clinical and medical characteristics of the study population

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    Table 3: Types of symptoms present in the symptomatic HCWs

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    Table 4: Types of comorbidities present in the study population

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    Table 5: Antibody response in all three samples (first, first follow-up, and second follow-up)

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    Table 6: Antibody response in different age groups in first sample

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    Table 7: Antibody response observed in different blood group HCWs (in first sample)

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    Table 8: Antibody response in the presence of comorbidity (in first sample)

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    Table 9: Antibody response in relation to occupational categories (in first sample)

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    Table 10: Antibody response in RAT and RT-PCR-positive groups (in first sample)

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    Table 11: Antibody response among symptomatic and asymptomatic HCWs (in first sample)

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    Table 12: Antibody response in relation to comorbidities (first follow-up sample)

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    Table 13: Antibody response in relation to occupational categories (first follow-up sample)

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    Table 14: Antibody response among symptomatic and asymptomatic HCWs (first follow-up sample)

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    Table 15: Antibody response among RAT +ve and RT-PCR +ve HCWs (first follow-up sample)

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    Table 16: Antibody response in relation to different age groups (second follow-up sample)

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    Table 17: Antibody response in relation to different blood groups (second follow-up sample)

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    Table 18: Antibody response in relation to presence or absence of comorbidities (second follow-up sample)

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    Table 19: Antibody response in relation to occupational categories (second follow-up sample)

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    Table 20: Antibody response in symptomatic and asymptomatic HCWs (second follow-up sample)

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    Table 21: Antibody response in RAT- and RT-PCR-positive HCWs (second follow-up sample)

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      Discussion Top


    The study was conducted among the HCWs of a tertiary care hospital during the first wave of SARS-CoV-2 pandemic.[1] The majority of HCWs participated in this study were within 20–29 years of age (48%) followed by 26% in the 30–39 years age group [Table 1]. The youngest HCW was 20 years and the oldest was 64 years. More male HCWs (69%) voluntarily participated in the study than female HCWs (31%). Doctors were enrolled in higher numbers (60%) than other HCWs such as laboratory technicians, nurses, cleaners, and so on.

    The medical history of the study group showed that they were predominantly symptomatic (92%) during the SARS-CoV-2-positive period. The more common symptoms were fever (74%), followed by body ache, cough, sore throat, and so on, followed by other less common symptoms such as nasal discharge, diarrhea, abdominal pain, and so on [Table 3]. There were two HCWs who had low SpO2 and required oxygen therapy during their treatment and both had diabetes as comorbidity. The presence of comorbidity was 20% which was inversely proportional to the younger age. The common comorbid health conditions were hypertension (36%), diabetes (20%), smoking (32%), alcohol consumption (36%), and so on [Table 4].

    We included both rapid antigen-positive and RT-PCR-positive HCWs to compare seroconversion between the two groups. The IgG antibody testing result showed 88% seroconversion among a total of 127 participants [Table 5]. The first sample was collected between 25th and 35th days of becoming SARS-CoV-2-positive. Seroconversion among RAT-positive category was higher (98.61%) than the seroconversion RT-PCR test-positive category of HCWs (74.55%) [Table 10]. Other studies published explained why positive RT-PCR test may not indicate true infection and hence fail to evoke response in the body. Although RT-PCR test can reliably detect causative viruses from respiratory secretions,[10] it is a marker of virus shedding, but it does not necessarily indicate the presence of viable virus.[11]

    The RT-PCR assay, which is the current standard test for laboratory diagnosis of SARS-CoV-2 infection, requires at least 4 h of operation to be performed by skilled technicians.[4] The cause of the rest, 25% of RT-PCR-positive participants’ failure to develop antibodies, is a matter of further discussion. It can probably be explained as the presence of non-viable SARS-CoV-2 and hence does not elicit immune response leading to failure in the development of antibodies. Another study published from this institute by Gogoi et al. in 2020 suggested that SARS-CoV-2 in low amount might be harbored transiently as bystander in droplet particles before being expelled from the nasal cavity, which can be detected by the highly sensitive RT-PCR test. They may be below the infectious dose that is necessary to cause a clinical or a sub-clinical infection and fails to illicit an immune response.[9]

    In the present study, SARS-CoV-2 antibody [IgG]-negative HCWs were dropped from the study once showed negative result in the first sample. Out of them, three participants were previously RT-PCR-positive and asymptomatic clinically and later they again became symptomatic and tested SARS-CoV-2-positive by RAT. The rapid assay for SARS-CoV-2 antigen detection (Standard™ Q COVID-19 Ag kit) showed comparable sensitivity [98.33%; 95% confidence interval (CI): 91.06–99.96%] and specificity (98.73%; 95% CI: 97.06–99.59%) with real-time RT-PCR assay. We believe that there is a potential use of this rapid and simple SARS-CoV-2 antigen detection test as a screening assay, especially in a high prevalence area.[5]

    The first follow-up (in an interval of 3 months) samples showed 93.85% of IgG positivity and the second follow-up samples which were collected after 6 month showed 88.24% SARS-CoV-2 IgG-positive antibodies. However, 11.76% became IgG antibody-negative who were initially positive. We again dropped the participants in the second follow-up who did not develop antibodies in the first follow-up. Our findings were similar to Turner et al.,[12] which showed that anti-S IgG antibodies in serum were detectable at least 7 months after infection in all 19 of the convalescent donors from whom they also obtained bone marrow aspirates to compare and confirm.

    Another objective of the present study was to correlate the seroconversion of symptomatic HCWs by the presence of IgG antibodies with that of asymptomatic HCWs. The symptomatic category showed higher (90.68%) seropositivity when compared with the asymptomatic group (55.52%) [Table 10]. Gogoi et al.,[9] in the investigation of suspected re-infection cases, found that no IgG antibody was there in the asymptomatic SARS-CoV-2-positive group during the first episode, even after 25–30 days of first infection. This finding is similar to other published studies conducted in other populations. Shirin et al.[13] emphasized that asymptomatic individuals do not develop antibody probably due to the low level of SARS-CoV-2, which is not enough to elicit immune response. The study by Long et al.[14] found that symptomatic cases have higher seroconversion than asymptomatic. A higher viral load may lead to more severe diseases and generate a stronger antibody response through increased levels of viral antigen.[15] These infections can reliably be detected by RAT screening method and they eventually lead to intense immune response and detection of antibody in blood tests.

    We did not find any positive correlation between any specific blood groups in getting SARS-CoV-2 infection or development of antibodies.

    Limitation of our study was that convenient sampling was done in the study and the study population was small. The smaller number of participants in the second follow-up was due to the starting of vaccination against SARS-CoV-2 among HCWs, which excluded them for being eligible. We also could not quantify the IgG antibody titer as the it was race against time to do the study and the funding was small. Other types of antibodies such as IgM and IgA could not be detected in the present study.


      Conclusion Top


    RAT-positive symptomatic people have more chance of development of effective immune response which could be evident by the detection of IgG antibodies within a month’s time and it remain sustained for more than six months in their blood.

    Acknowledgements

    The authors acknowledge Sunia Roy, Babita Saikia, Rekha Barman, Rashmi Roy, technicians, and staff who contributed by sample collection and testing.

    Financial support and sponsorship

    Multidisciplinary Research Unit, Assam Medical College and Hospital, Dibrugarh, Assam, India.

    Conflicts of interest

    None.

    Ethical policy and Institutional Review Board statement

    Reviewed and approved by Institutional Ethical Clearance.

    Patient declaration of consent statement

    Yes.

    Data availability statement

    The data set used in the current study is available on request from Dr Gayatri Gogoi and Dr Mithu Medhi.

     
      References Top

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    Li Q, Guan X, Wu P, Wang X, Zhou L, Tong Y, et al. Early transmission dynamics in Wuhan, China, of novel coronavirus-infected pneumonia. N Engl J Med 2020;382: 1199-207.  Back to cited text no. 1
        
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    Razzini K, Castrica M, Menchetti L, Maggi L, Negroni L, Orfeo NV, et al. SARS-CoV-2 RNA detection in the air and on surfaces in the COVID-19 ward of a hospital in Milan, Italy. Sci Total Environ 2020;742:1-7.  Back to cited text no. 3
        
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    Shirin T, Bhuiyan TR, Charles RC, Amin S, Bhuiyan I, Kawser Z, et al. Antibody responses after COVID-19 infection in patients who are mildly symptomatic or asymptomatic in Bangladesh. Int J Infect Dis 2020;101:220-5.  Back to cited text no. 4
        
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    Long QX, Tang XJ, Shi QL, Li Q, Deng HJ, Yuan J, et al. Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections. Nat Med 2020;26:1200-4.  Back to cited text no. 5
        
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    Turner JS, Kim W, Kalaidina E, Goss CW, Rauseo AM, Schmitz AJ, et al. SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans. Nature 2021; 595:421-5.   Back to cited text no. 7
        
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    Lai X, Wang M, Qin C, Tan L, Ran L, Chen D, et al. Coronavirus disease 2019 (COVID-2019) infection among health care workers and implications for prevention measures in a tertiary hospital in Wuhan, China. JAMA Netw Open 2020;3: e209666.  Back to cited text no. 8
        
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    Iwasaki A, Yang Y. The potential danger of suboptimal antibody responses in Covid-19. Nat Rev Immunol 2020;20:339-41.  Back to cited text no. 9
        
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    Chaimayo C, Kaewnaphan B, Tanlieng N, Athipanyasilp N, Sirijatuphat R, Chayakulkeeree M, et al. Rapid SARS-CoV-2 antigen detection assay in comparison with real-time RT-PCR assay for laboratory diagnosis of Covid-19 in Thailand. Virol J 2020;17:177.  Back to cited text no. 10
        
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    Wang X, Guo X, Xin Q, Pan Y, Hu Y, Li J, et al. Neutralizing antibody responses to severe acute respiratory syndrome coronavirus 2 in coronavirus disease 2019 inpatients and convalescent patients. Clin Infect Dis 2020;71:2688-94.  Back to cited text no. 11
        
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    Otter JA, Donskey C, Yezli S, Douthwaite S, Goldenberg SD, Weber DJ. Transmission of SARS and MERS coronaviruses and influenza virus in healthcare settings: The possible role of dry surface contamination. J Hosp Infect 2016 ;92:235-50.  Back to cited text no. 12
        
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    Corman VM, Landt O, Kaiser M, Molenkamp R, Meijer A, Chu DK, et al. Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR [published correction appears in Euro Surveill 2020 Apr;25(14)] [published correction appears in Euro Surveill 2020 Jul;25(30)] [published correction appears in Euro Surveill 2021 Feb;26(5)]. Euro Surveill 2020;25:2000045. doi:10.2807/1560–7917.ES.2020. 25.3.2000045.  Back to cited text no. 13
        
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    Hou H, Wang T, Zhang B, Luo Y, Mao L, Wang F. Detection of IgM and IgG antibodies in patients with coronavirus disease. Clin Transl Immunol 2020;9:e1136.  Back to cited text no. 15
        



     
     
        Tables

      [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11], [Table 12], [Table 13], [Table 14], [Table 15], [Table 16], [Table 17], [Table 18], [Table 19], [Table 20], [Table 21]



     

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