Introduction
Most of the published studies have demonstrated a highly variable seroprevalence rate of SARS-CoV-2 IgG antibodies in health care workers [HCW’s] across the globe during the pandemic period which clearly indicates a high impact of various socio demographic factors.1, 2 In this context many authors have investigated multiple risk factors that were supposed to influence the seropositivity in HCW’s. 1, 2 The overall seroprevalence from various independent, systematic studies and scoping reviews has been shown to be in the range of 0.1- 46% in developing countries especially from south Africa. 1, 2 Studies from various geographic regions of India has demonstrated seropositivity in the range of 1-26%.3, 4 Seroprevalence studies aims to determine the proportion of HCW’s who had been exposed to infection irrespective of the symptoms, the level of exposure and identifying the high-risk locations and the professionals within the health care system. It helps the hospital administration to avoid unnecessary quarantines in times when there is dearth of staff, and also help plan appropriate use of health care resources. Clarity on the immunological response to SARS-CoV-2 is still under study; the exact time of seroconversion, the levels of antibody produced are still not well understood. Moreover, the correlation between seropositivity, antibody levels, protection against reinfection and duration of protective immunity remains a gray zone. 5
Aim & Objective
The primary aim of the study was to determine the seroprevalence of SARS-CoV-2 IgG in health care workers in local settings during the pandemic period. The secondary objectives being to determine seroprevalence in two different groups of health care workers as symptomatic and asymptomatic. In addition to determine the relation between the various risk factors and seropositivity amongst these group of HCW’s.
Materials and Methods
Study type
Cross sectional prospective study on health care workers at a tertiary care health center.
Study period and place
One month; from March 2021-April 2021 at a tertiary health care center and teaching hospital of Ayaan institute of medical sciences and research center Kankamamidi village, RR district, Telangana state in south India.
Sample size
Sample size estimated usinginformation on seroprevalence from already published studies ranging between 10% -26% at a CI. of 95% and a precision of 5%.
Inclusion criteria
Health care workers above 18 years of age, who are recruited through HR department on permanent basis and are on regular duties during the pandemic period. Those who are not vaccinated against SARS-CoV-2 and didn’t have rt RT-PCR confirmed COVID-19 disease in the recent past 14 -21days before the sampling time as the study aimed on determining seroprevalence of SARS-CoV-2 IgG and not on the incidence of disease or diagnosing acute infection. Participants were grouped into symptomatic and asymptomatic based on the history of presence of symptoms of COVID-19 disease in the past 3-6 months according to WHO clinical grading of the disease as mild, moderate and severe disease and documented in the questionnaire admitted. Results of detection of SARS-CoV-2 RNA by rt RT-PCR 3- 6 months before if available from the symptomatic group were recorded from the documented questionnaire. Risk assessment for work place-based exposure was done using CDC guidelines on healthcare personal risk assessment on exposure to COVID-19 patients and participants were grouped as high risk, intermediate or medium risk and low risk group based on the information documented by them in the questionnaire.6, 7 IERB clearance was obtained prior to the study.
Data collection
Descriptive data was collected from the participants on sociodemographic factors like, age, gender, professional category, risk group, travel history and presence of comorbid conditions, having COVID-19 confirmed disease, and history of vaccination against it using validated questionnaire.
Statistical tools used
Chi-square test and unpaired student t test and Fisher exact test were applicable using R language software.
Test performed
5ml blood samples was collected under aseptic precautions in gel tube from BD India and tested for SARS-CoV-2 antibodies using ELFA technology from Biomerieux India.
Principle of the test
Is a qualitative /semiquantitative sandwich assay wherein anti spike protein antibodies [RBD] to SARS CoV-2 was detected using recombinant spike protein antigen and antihuman IgG conjugated with alkaline phosphate enzyme which hydrolyzes the fluorescent substrate [4 methyl umbelliferon phosphate] to 4 methyl umbelliferon; the fluorescence of which was proportional to the amount of antibody in the test sample. The sensitivity of the assay was 100% and specificity as almost 99.98%.
Interpretation
The sample relative fluorescence is measured as index value and the assay cutoff value of ≥1 was taken as positive and <1.0 as negative as mentioned by the manufacturer 8
Results
Around 141 HCW’s were included out of the 230 enrolled. Three participants who were rt RT-PCR positive for SARS-CoV-2 RNA in recent past i.e., 14-21 days from the sampling time and 86 who were vaccinated against COVID-19 were excluded from the disease. Overall seropositivity noted was 48/141 (34.04%). In symptomatic group we had 19 /72 (26.38%) seropositive subjects and in asymptomatic we had 29/69 (42.02%).
Gender
With respect to gender the male to female ratio in the study participants was noted as 1.2:1 i.e.; 77/64. The female gender had higher seropositivity in overall and in symptomatic group of subjects but in asymptomatic HCW’s males predominated as shown in (Table 1, Table 2, Table 3 ).
Age
In the present study the age range of HCW’s was between 20-80 years. Maximum no. of participants in descending order of frequency were observed in the age range of 21-30 years, followed by 31-40, 41-50, 61-70, 51-60, and 71-80 years shown in Table 1. The overall mean age of the participants was noted as 39.01 ±13.04. The mean age for symptomatic group was greater as 41.16 ± 14.27 compared to asymptomatic group as 36.68 ± 11.19 with a p value of 0.04 and t test value of 2.06. gender wise when checked, the mean age for symptomatic males was greater as 43.18 ±14.03 compared to asymptomatic males 39.37 ±12.48 with p value of 0.22 and t value of 1.24. In females the mean age of the symptomatic was greater than asymptomatic group as 36.65 ±13.79 vs.34.58 ± 9.29 with p value of 0.48 and t value of 0.72. Similar pattern of age distribution was observed with respect to gender in seropositive and seronegative subjects in symptomatic and asymptomatic participants with symptomatic participants being greater in age than asymptomatic participants. Overall seropositivity was observed to be higher as 15/30 [50%] in the age group 41-50 years. However, the findings differed when the symptomatic and asymptomatic HCW’s where compared. Highest seropositivity of 50% was observed in the age group 51-60 years in symptomatic and 100% seropositivity in asymptomatic as 2/2 in the age group 61-70 years as shown in (Table 1, Table 2, Table 3).
Symptomatic health care workers
Of the 72 [51.06%] symptomatic participants 71 (98.61%) experienced mild influenza like illness with symptoms of upper respiratory tract infection like cough, cold, mild fever, myalgia, loss of taste and loss of smell sensation. Only 1 (1.29%) of the participant had moderate disease with symptoms of pneumonia and required hospitalization. Of the 72 participants 23 (31.94%) gave history of undergoing SARS-CoV-2 RNA by rt RT-PCR in the past 3-6 months and 3 (13.04%) of them were detected positive. The remaining 49 (68.05%) didn’t reveal any information on the diagnostic test they underwent. However, they experienced ILI symptoms. Of the symptomatic participants only 19 (26.38%) were seropositive for IgG antibodies as seen in (Table 3).
Asymptomatic health care workers
Were around 69 [48.93%] and of which 29(42.02%) were seropositive for IgG antibodies. Except for the age group 31-40 and 51-60 years and presence of travel history as risk factors, asymptomatic HCW’s were seropositive in greater number than symptomatic health care workers.
Risk category
According to the CDC risk assessment category of HCW’s for covid-19 disease we had majority of the HCW’s in high-risk group as 62/141 (43.97%) followed by intermediate /medium risk group as 42/141 (29.78%) and low risk group as 37/141 (26.24%). Overall highest seropositivity was noted in the intermediate risk group as17/42 (40.47%) with similar observation in asymptomatic group of HCW’s as 11/20 (55%). However, in symptomatic group of participants maximum seropositivity was noted in high-risk group as 10/36 (27.77%) as shown in (Table 1, Table 2, Table 3).
Comorbid conditions
The common comorbid conditions observed in HCW’s in descending order of frequency are diabetes mellitus [DM], hypertension [HTN], asthma. Very few of them documented presence of neurological disorder and immunosuppression. Some even had a combination of two to three disorders together like DM with HTN or DM with HTN and asthma. Around 22/141 (15.60 %) had comorbid conditions of which 15/72 (20.83%) were in symptomatic and 7/69 (10.14%) in asymptomatic group. Of the 15 symptomatic HCW’s with comorbid conditions, 6 members had DM of which 2 were seropositive and of 4 with asthma one was seropositive, of the remaining five, 2 with DM and HTN, another 2 members with DM, HTN and asthma and one with neurological deficit all were seronegative. In asymptomatic subjects of the total 7 subjects with comorbidity, 4 members had DM and hypertension of which one was seropositive and of the 2 hypertensive subjects one was seropositive, one with asthma was seronegative as seen in (Table 1, Table 2, Table 3).
Table 1
Overall SARS-CoV-2 IgG antibody sero positivity in HCW’s against the various risk factors studied.
Table 2
SARS-CoV-2IgG antibody seropositivity in symptomatic HCW’s
Table 3
SARS-CoV-2 IgG antibody seropositivity in asymptomatic HCW’s
Table 4
Comparison of SARS-CoV-2 IgG seropositivity for the various risk factors studied between symptomatic and asymptomatic health care workers
Table 5
Comparison of seroprevalence rates for SARS-CoV-2 IgG antibodies in asymptomatic group of health care workers from previous studies.
Travel history
Travel to high prevalence zones of covid -19 confirmed cases at international, national and local level was noted in 19/141 (13.47%) HCW’s of which 12/72 [16.66%] were in symptomatic group and 7/69 (10.14%) were in asymptomatic group. Of this 3/19 (15.78%) were seropositive and 2/12 (16.66%) in symptomatic group and 1/7 (14.28%) in asymptomatic group as seen in (Table 1, Table 2, Table 3).
When the two groups of HCW’s symptomatic and asymptomatic were compared for the association of risk factor with IgG seropositivity to SARS-CoV-2. Overall, the asymptomatic participants were seropositive in greater number than symptomatic for most of the risk factors studied except for the age group 31-40 years and 51-60 years of age wherein a greater number of symptomatic HCW’s were seropositive as 4/21 (19.09%) against 3/17 (17.64%) and as 3/6 (50%) against 0/5. Similarly, when checked for presence of travel history more of the symptomatic HCW’s were seropositive than asymptomatic as 2/12 (16.66%) against 1/7 (14.28%).
Discussion
The overall seroprevalence of SARS-CoV-2 IgG antibodies in the present study is noted as 34.04% which is similar to the reports by other authors as 33%. 9, 10 In the present study greater number of asymptomatic HCW’s as 42.02% were seropositive than symptomatic ones as 26.38% which has been observed in other studies too9, 10, 11, 12, 13, 14, 15, 16, 17, 18 and summarized in the (Table 5) for comparison purpose.
Presence of greater no. of seropositive for SARS-CoV-2 IgG in asymptomatic group of HCW’s can be explained for reasons like:
Silent transmission from pre symptomatic and asymptomatic subjects to the susceptible HCW’s. 12, 13, 14, 15, 16, 19
The period of study also matters, as most of the studies conducted so far were during the 1st wave of the pandemic were in the clarity on time required for development of demonstratable humoral immune response and its duration was vague. The present study was done during the 2nd wave which might have resulted in generation of good humoral immune response following repeated and mild exposures to the virus as reported by other authors too.14, 15
Presence of preexisting’s antibodies to circulating HCoV’s like HKU-1, OC-43, NL63, 229E etc. during the annual seasonal outbreaks of ILI might have resulted in seropositivity in asymptomatic group due to cross reactive antibodies against spike protein, NTD & RBD and N protein and also for the presence of reactive T cells to SARS-CoV in the pre pandemic samples as demonstrated by one author in his original research study.20
Effective training and education, implementation and monitoring of infection control practices among the symptomatic and HRG of subjects with resultant lower exposure rates and less seropositivity and suboptimal assurance of same in IRG & LRG category of HCW’s as reported by many authors.1, 2, 13, 14
Exposure to confirmed cases of COVID-19 disease outside the hospital premises could also be a reason for high seropositivity.9, 10, 11, 12, 13, 14, 15, 16
Greater no. of HCW’s in the middle age group were seropositive in symptomatic group when compared to asymptomatic group wherein it was found to be highly variable and in descending order of frequency, maximum participants were observed in the age group 61-70 years, followed by 41-50 years and then in age group of 21-30 years. However, most of studies have related seropositivity with increasing age and more so above 50 years of age 16, 17, 19 which is observed by us too as overall finding. In symptomatic group greater no. of HCW’s in HRG were seropositive while in asymptomatic it is observed in medium or IRG as shown in Table 1, Table 2, Table 3 and also reported by other authors which is related with the type of occupational exposure and personal observation and adherence to infection prevention and control measures by them.19 The most common comorbid condition associated with seropositivity in our study are diabetes mellitus, hypertension and asthma. Presence of comorbid conditions in HCW’s was significantly associated with higher seropositivity especially in asymptomatic HCW’s in our study. This has been well explained by previous authors by demonstration of polyfunctional helper CD4 cells and antibodies and variations in innate immune response in activation of T helper cell response in the sera of HCW’s studied.1, 2, 9, 10, 21 Majority (97.92%) of the symptomatic HCW’s had mild form of disease while only 1.38% had moderate disease as pneumonia and required hospitalization as seen in (Table 2) and observed by other authors too. 1, 2, 3 In Table 4 above we have compared the two groups of HCW’s for the risk factor association with seropositivity using statistical test like chi square and fisher exact test. None of the risk factors studied showed any positive association with seropositivity when two groups were compared indicating that no individual group had any specific high or low risk of getting seropositive to SARS-CoV-2 and demands further enquiry into its causal relationship with more improved testing strategy like determination of baseline and follow up titres of IgG antibodies to get clarity on genuine exposure and avoid unnecessary quarantines when there is significant dearth of HCW’s.
Conclusion
The results of present study indicate greater proportion of asymptomatic transmission of the infection in HCW’s during the pandemic which possess a substantial risk of infection to other healthy staff, vulnerable patients in the hospital setting and their families22, 23, 24 with its recommendations and limitations mentioned below.
Recommendations
Results of the present study warrants periodic testing, education and training of all HCW’s irrespective of the risk category, presence of symptoms, prioritization for vaccination and adequate supply & uniform distribution of PPE and education on its use to mitigate source and curb onward transmission of SARS-CoV-2 infection.1, 2, 22, 23, 24 Further studies determining seroprevalence rates in symptomatic and asymptomatic groups of participants need paired sera testing.
Limitations
The results of the present study couldn’t be generalized for reasons like we failed to perform baseline and follow up sampling of the HCW’s for demonstrating true exposure and fourfold rise in IgG titre. The major constraints noted were financial and apprehension of health care workers with resultant seropositivity and even sample size studied is too small for the purpose.
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