Seroprevalence of IgG Antibody Against SARS-Cov-2 Among Health Care Workers of Shimoga Institute of Medical Sciences, Shivamogga, Karnataka

Introduction

Severe Acute Respiratory Syndrome corona virus-2 (SARS-CoV-2) is a virus that belongs to the family Coronaviridae that causes Corona virus disease 2019 (COVID-19), which was accountable to Public Health Emergency of International Concern and ongoing COVID-19 pandemic. SARS-CoV-2 is a virus renowned to have zoonotic origin, suggesting it might have emerged from bat.¹ As of 23rd May 2021, WHO reported 166,346,635 confirmed cases globally and 3,449,117 deaths due to COVID-19.² SARS-CoV-2 is a single stranded (positive-sense) RNA virus associated with proteins which include spike (S), envelope (E), membrane (M) and nucleocapsid (N).³ Protein-N attributes to the proliferation of virus and interferes with the host cell cycle. Protein-S constitutes two functional subunits, where S1 (subunit 1) is responsible for binding to the host cell receptor and S2 (subunit 2) for fusion of the viral and cellular membranes.⁴ Chang et al., stated that the receptor binding domain (RBD) of S1 subunit will get fused and may induce a generation of neutralizing antibodies in the host.⁵ In general, N and S proteins are most immunogenic in nature and they are used to determine the primary and secondary immunological response to SARS-CoV-2.⁶ In general, primary immune response is mediated by IgM antibodies and small amount of IgG, which are detectable after seven days of infection and remains in serum for several weeks, whereas secondary immune response is mediated largely by IgG antibodies, which are detectable after the second week of infection and persists for several months. Due to lack of existence of primitive immunity in humans, SARS-COV-2 has emerged as a pandemic in December 2019.⁷ Despite having adequate resources for safety and care, health care workers are considered a high-risk group population for SARS-COV-2 infection as the rate of direct exposure is more.

The point prevalence study would be an effective method to understand the status of infection spreading in this particular population and would be instructive in policy making.⁸ This kind of study helps to acquire knowledge about the total number in the study population who had been infected, including those who might have missed early diagnosis.⁹ Thus it determines the exposure to the virus in past and describes the immune response to the infection.

The aim of the present study was to evaluate the prevalence of SARS-COV-2 infection among frontline health care workers (HCW) by determining the IgG antibody. This will help in understanding the rate of transmission in the population of HCW and provides better opportunity to understand asymptomatic cases of infection in HCWs and also assists for better arrangement of hospital settings in response to the COVID-19 pandemic.

Methods

This study was conducted at a teaching hospital attached to medical institute which was a 960-bedded referral center. The study was conducted from 18th September 2020 to 3rd November 2020 to evaluate the dynamics of SARS CoV-2 seroprevalence among all health care workers (HCWs) who were working in COVID and non COVID areas of the hospital. The study was conducted according to the ICMR and CDC guidelines.^10-11

The HCWs participated in the study on a voluntary basis and a written informed consent was taken. The study was started after obtaining the permission from institutional ethics committee. All the participants were given questionnaires regarding demographic and occupational data regarding nature of work (whether they worked in COVID isolation wards, COVID ICUs, other high risk areas or non COVID areas), nature of exposure (whether they were exposed to COVID patients in the hospitals and/or been in contact with relatives or friends with suspected COVID-19), symptoms experienced related to COVID-19 (fever, maylgia, fatigue, sore throat, conjunctivitis, gastrointestinal symptoms, anosmia/ dysguesia, cough and dyspnea), whether they had tested positive for COVID-19 by RT-PCR and whether they had co-morbid conditions etc. The confidentiality of the participant’s information was maintained.

After obtaining consent from participants, 5 mL of venous blood was collected from cubital vein with all aseptic precautions. The serum was separated by centrifugation and subjected to estimation of SARS CoV2 IgG antibodies by Chemiluminiscence Immunoassay (CLIA) by Beckman Coulter machine using Access SARS CoV-2 IgG kit which is approved by USA FDA. This is based on the principle that recombinant SARS CoV-2 protein specific for the receptor binding domain (RBD) of the S1 protein is used as antigen which binds to SARS CoV-2 antibodies. The results were interpreted qualitatively according to manufacturer’s protocols as shown in Table 1.

Access SARS CoV-2 Assay offers highest sensitivity of about 100% and specificity of nearly 99.8%.

Data was analyzed using SPSS software. We estimated prevalence with 95% confidence limits of serological positivity for SARS-CoV-2 IgG antibodies. We estimated statistical significance for the different variables using Chi-square test. P value at 0.05 was considered significant.

Results

Six hundred and seventy-two participants were enrolled for the study. The response rate of the participants was 74.66% (672/900). The participants included 197 doctors, 92 interns, 44 post graduate students, 150 staff nurses, 48 lab technicians and 141 group D workers. Out of 672 participants, 180 (26.80%) were reactive for SARS CoV-2 antibodies. (Table 2)

Among 672 HCWs, 341 (50.74%) were male and 331 (49.25%) were female. Out of 672 HCW participants, 30 (4.46%) gave history of co-morbid conditions like diabetes mellitus, heart diseases, kidney diseases, allergic diseases etc. Seventy-eight (11.60%) were symptomatic who gave history of fever, cough, myalgia, loss of taste and smell etc. In this study, 52 (7.73%) RT-PCR positive HCWs had symptoms of COVID-19. Majority of HCWs i.e., 636 (94.64%) came in contact with COVID-19 patients in the hospital during their care and the rest 22 (3.27%) contacted COVID-19 patients in their family setting. (Table 3)

The highest prevalence rate of 40% (72/180) was noted in the age group of 18-30 years, followed by 28.33% (51/180) in 31-40 years, 22.22% (40/180) in 41-50 years, 8.88% (16/180) in 51-60 years and 0.55% (01/180) in >60 years. Not many differences related to sex were noted as it was 45.55% (82/180) among females and 54.44% (98/180) among males.

Based on the work category, seroprevalence was highest among nursing staff 29.44% (53/180), followed by doctors 23.88% (43/180), group D workers 23.33% (42/180), Lab technicians 11.11% (20/180), Interns 7.77% (14/180) and Post graduate students 4.44% (8/180). Co-morbid conditions were evident in about 16.66% (30/180) of the participants. None of the participants who were reactive for SARS CoV -2 IgG antibodies gave history of hospitalization.

Seventy eight of 672 HCWs claimed to have suffered COVID-19 related symptoms. Among those 78 HCWs, 10 (5.55%) were reactive for SARS CoV-2 IgG antibodies.

All 52 (7.73%) participants who showed RT-PCR positive were also reactive for the SARS CoV-2 IgG antibodies. Out of 672, 636 HCWs gave history of contact with COVID-19 patients in the hospital during their patient care. Of these 636 HCWs, 168 (93.33%) were seropositive for SARS CoV-2 IgG antibodies and among 672 HCWs, 22 gave history of contact with COVID-19 patients during their care in the family of which 10 (5.55%) were reactive for the SARS CoV-2 IgG antibodies. (Table 4)

HCWs working in isolation wards showed highest seroprevalence, i.e. 43.88% (79) followed by other high risk areas 28.33% (51) and ICUs 24.44% (44). Seroprevalence among those working in other non COVID areas like administration zone was least 3.33% (6).

Discussion

The seroprevalence study of SARS-CoV-2 IgG antibodies plays an important role to assess the impact of pandemic on the health care workers. We can study the prevalence of SARS-CoV-2 IgG antibodies among the HCWs; in turn we can assess the exposure and also estimate the humeral immune response of our HCWs. Since we don’t have the statistics of seroprevalence among local population, comparison could not be done with seroprevalence among HCWs, which indirectly assesses the efficiency of infection control practices and safety protocols.

This study was done to know the seroprevalence of SARS-CoV-2 IgG antibodies among the HCWs which revealed 26.8% (180/672) of the participants were having the circulating antibodies. Even though there was strict application of safety protocols and infection control practices in our clinical setting, the results among HCWs were slightly higher compared to other studies. Many studies have been published on seroprevalence among HCWs with varied outcomes depending on various factors like age, gender, areas of work and associated co-morbid conditions.

An overall 8.7% seroprevalence of SARS-CoV-2 IgG antibodies has been evidenced among the HCWs.¹² Laura Milazzo et al.,¹³ in Italy conducted a study on dynamics of seroprevalence and found that seroprevalence had increased from 0.5% to 5.4% over a period of two months. Our study is in concordance with the results of study conducted in United Kingdom by Denis Mukwege et al.,¹⁴ where the seropositivity rate was 18.7% for SARS -CoV-2 IgG antibodies. A study conducted at Lokamanya Tilak Municipal General Hospital, Mumbai, India, recruited 501 HCWs from COVID area and 1051 HCWs from non-COVID areas,¹⁵ showed an overall seroprevalence among all the HCWs as 6.9%. A systemic review and meta-analysis study conducted to detect the seroprevalence of SARS-CoV-2 IgG antibodies among the HCWs in Europe, USA and East Asia revealed, a seroprevalence ranging from 0.3% to 32.6%.16 Many studies in this meta-analysis were of the opinion that HCWs suffer a significant risk of COVID-19 from the hospital environments. It was also stated that seroprevalence among HCWs was much higher than general population.

Our study revealed that higher rate of prevalence noted in younger (18-30 years) age group HCWs, was probably due to their frequent visit to high risk areas and also better immunogical response among them. In contradictory to our observations, Sujata Bhaveja et al.,15 reported a significantly higher seropositivity among people aged more than 50 years.

This study has reported higher rate of infection among nursing staff (29.44%), doctors (23.88%), and Group D workers (23.33%) compared to Lab technicians and it is in concordance with the previous reports.¹⁵ This is probably due to their direct exposure to COVID-19 patients in the hospital. Higher rate of infection was noted in HCWs working in COVID isolation wards (43.88%) compared to other high risk areas (24.44%) and ICUs (24.44%). A meta-analysis study conducted by Ahmed Hossain et al., ¹⁶ also found that HCWs working in high risk in-patient settings had a higher prevalence of IgG antibodies compared to those working in low risk areas. The present study has noted a higher prevalence of infection among asymptomatic HCWs (94.44%) compared to symptomatic HCWs (5.55%). This warrants a need for surveillance of all asymptomatic HCWs regularly so that both patients and HCWs can be protected from possible health care associated transmission of SARS-COVID-19 virus.

This higher rate of infection could be due to transmission from patient to HCWs and HCWs to HCWs, because of low compliance to use PPE kit, inappropriate doffing and poor adherence to infection control measures. This highlights the importance of proper application and scientific removal of PPE kit in doffing room, universal masking and absolute adherence to infection prevention & control measures so that health care associated transmission of SARS-CoV-2 can be reduced. By adhering to hospital safety protocols, we can reduce the transmission of infections from HCWs to community, particularly when HCWs are asymptomatic.

Limitations of the study

There was poor compliance to follow-up of HCWs who were reactive to SARS-CoV-2 IgG antibodies. Hence, we could not study the dynamics of seroprevalence among the HCWs over a period of time.

Conclusion

In our study, we noted a higher rate of infection among HCWs because of improper doffing procedure and poor adherence to hospital infection control policies. Hence, emphasis should be given to scientific procedure of doffing, universal masking and strict adherence to hospital infection control policies to prevent the health care associated transmission of SARS-CoV-2.

Conflicts of interest

None.