key: cord-0880010-26v9lgnt
authors: Eldesoukey, Nermeen; Gaafar, Taghrid; Enein, Azza Aboul; Eyada, Iman; Khirat, Sahar; ElShahawy, Asmaa; Diaa, Nehal; Youssry, Ilham
title: SARS‐CoV‐2 antibody seroprevalence rates among Egyptian blood donors around the third wave: Cross‐sectional study
date: 2022-05-12
journal: Health Sci Rep
DOI: 10.1002/hsr2.634
sha: 4e52117fdcdfba35c5f9d93a7ec1d5eb6b4759d1
doc_id: 880010
cord_uid: 26v9lgnt

BACKGROUND: Seroprevalence studies may provide a more representative situation of the disease burden and population‐level immunity in a country. AIM: The aim of this study was to determine the prevalence of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) antibodies among asymptomatic blood donors attending the Cairo University blood bank services at various points in time around the third wave. METHODS: This cross‐section study included 3058 eligible blood donors, representing a demographically and socially heterogeneous healthy population and categorized as: Group 1, 954 donors in the period from March 20 to 30/2021; Group 2, 990 donors in the period from June 3 to 10/2021. These two groups were tested for IgG against SARS‐CoV‐2 nucleocapsid antigen (NC) to detect qualitative reactivity. Group 3, 1114 donors in the period from July 20 to 30/2021 were tested by the SARS‐CoV‐2 IgG II Quant assay for the quantitative detection of IgG antibodies, including neutralizing antibodies (antispike antibodies). RESULTS: Donors' age ranged between 18 and 59 (mean 33.9 ± 9) years. There was no significant correlation between seroprevalence and gender, area of residence, ABO or Rh blood types, and occupation or education. Antibody prevalence was found to be 13.2% in Group 1, 19.2% in Group 2 (overall 16.2%), and 66% in Group 3. There were only 49 included cases vaccinated against COVID‐19. CONCLUSION: We concluded that the significant increasing trend in seroprevalence rates during the third wave, March, June, and July, in Egypt, reflects a high cumulative incidence of seroconversion that mirrored the epidemic curve in its rise, fall, and nadir.

On the 11th of March 2020, the World Health Organization declared COVID-19 to be a global pandemic. 1 The particular coronavirus responsible for this pandemic is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). 2 Since the beginning of the pandemic, there were controversial views about the infectiousness of asymptomatic patients. It was reported that approximately 40%-45% of patients will remain asymptomatic. Knowing the seroprevalence rates of SARS-CoV-2 among apparently healthy asymptomatic individuals is important in determining the fraction of a population that may constitute a significant source of virus transmission.

Earlier on within the pandemic, a global survey for determining seroprevalence rates had been carried out in 48 participating blood transfusion centers. This allowed for tracking of infection rates in donors over time. Such surveys are done for the purpose of directing public health policies and implementing strategies for the reduction of viral transmission. 3 Seroprevalence studies may provide a more representative situation of the disease burden and population-level immunity in a country. These studies may play an important role in ensuring that the health system in a country remains operative without failure and may help in making decisions for the procurement of adequate doses of vaccines. 4 Several studies addressing the issue of host humoral immune response to SARS-CoV-2 among COVID-19-confirmed patients have been published. 5, 6 It is now well accepted that total antibody to SARS-CoV-2 (T Ab) is the earliest and most sensitive serologic biomarker, rising from 1 to 2 weeks of symptom onset, and thereon, all patients remained reactive. IgM and IgG seroconversion occurs usually in the second or third week, where there is a quick decline of IgM levels and a longer persistence of IgG. Antibodies to nucleocapsid antigen (NC) are more abundant and decay more quickly, 6 while antibodies to spike receptor-binding domain (RBD) (S) inhibit binding to ACE2 receptor, hence generating a strong viral-neutralizing response and viral clearance. 7 Currently, there is not much available data on serologic screening of asymptomatic people. Published data showed that seroprevalence of SARS-CoV-2 antibodies ranged from 1.6% to 4.1% among different populations. 8-10

The aim of this study was to determine the prevalence of SARS-CoV-2 antibodies among asymptomatic blood donors who attended the Cairo University blood bank (CUBB) services at various points in time (during the third wave of the COVID-19 pandemic and beyond).

A cross-sectional study consisting of serological testing for SARS-CoV-2 in healthy asymptomatic volunteer blood donors attending CUBB.

The study subjects included all eligible donors who attended CUBB for blood donation at the time in which the kits for SARS-Cov-2 antibody testing are available. They were demographically and socially heterogeneous healthy population from different areas of Egypt because CUBB is considered the biggest blood bank, which serves all Cairo University hospitals and is a referral hospital from all over Egypt. 

The plasma samples used for mandatory testing in the donated units were also used for SARS-CoV-2 antibody testing. At the beginning of blood donation, samples were collected and barcoded for each donor.

For study Groups 1 and 2, the Abbott Architect SARS-CoV-2 IgG assay (chemiluminescent microparticle immunoassay) was used, which was the antibody assay available at the time in our center.

This assay measures IgG against the SARS-CoV-2 and was used to detect qualitative reactivity. Based on the manufacturer's recommendation, a cut-off ratio of ≥1.4 was considered positive.

For study Group 3, the Abbott SARS-CoV-2 IgG II Quant assay was used for the qualitative and quantitative determination of IgG antibodies, including neutralizing antibodies, to the RBD of the S1 subunit of the spike protein of SARS-CoV-2 in plasma (Antispike antibodies). This was the assay method introduced later in the study.

The sample cut-off was 50 AU/ml (arbitrary units per milliliter). 11,12

Data were tabulated in an Excel spreadsheet, with donor demographic characteristics reported by code, so that their individual identity would remain anonymous.

Data were analyzed using SPSS version 24: for the qualitative variables, the percentage was used, while the mean and standard deviation was used for quantitative variables. χ 2 was used to determine whether there is a statistically significant difference between the observed frequencies in the studied groups. The level of significance was p < 0.05.

The overall seroprevalence was 34.43% (1053 subjects out of 3058 studied cases). They were categorized as: Group 1: Nine hundred and fifty-four donors in the period from March 20 to 30/2021. Group 2: Nine hundred and ninety donors in the period from June 3 to 10/2021 were tested for IgG against SARS-CoV-2 nucleocapsid antigen (NC) to detect qualitative reactivity. The antibody prevalence was found to be 13.2% and 19.2%, respectively, in the studied Groups 1 and 2 ( Figure 1 ). The overall prevalence of antibodies in those two batches was 16.2% with a minimum qualitative index > 1.4. The mean ± SD antibody level is shown in Table 1 .

Group 3: One thousand one hundred and fourteen donors in the period from July 20 to 30/2021 were tested by the SARS-CoV-2 IgG II Quant assay for the quantitative detection of IgG antibodies, including neutralizing antibodies to the RBD of the S1 subunit of the spike protein of SARS-CoV-2 in plasma. The seroprevalence rate was 66%. The mean ± SD antibody level is shown in Table 1 and Figure 1 .

The characteristics of the included blood donors (for all groups) are summarized in Table 2 . There were significantly more males than females in the studied population. The ages ranged between 18 and 59 years with a mean of 33.9 ± 9.

There was no significant correlation between seroprevalence and gender, area of residence, ABO or Rh blood types, and occupation or education. The characteristics of the 49 vaccinated studied donors were shown in (Table 3) . Most (73.5%) of the vaccinated population had a higher education than the nonvaccinated cases ( during June, and 66% during July (p < 0.001) (Figure 1 ). This trend mirrors the World Health Organization (WHO) epidemic curve, where the curve has been shown to be on the rise during March, April, and May, and then it started a downwards trend in June. The nadir was reached by the end of July. 13 

To date, this is the first large study in Egypt addressing the seroprevalence of SARS-CoV-2 in asymptomatic, healthy blood donors in CUBB.

Since the evolution of the pandemic, many countries applied screening of COVID-19 antibodies, as an indication of immunity acquired by naturally exposed or vaccinated individuals. SARS-CoV-2 seroprevalence studies are thus fundamental to effectively monitor the extent of the COVID-19 epidemic and support authorities in making informed decisions.

Blood bank infrastructure allows rapid feasible random screening of regional populations to monitor seroprevalence. To collect samples from adults above 18 years is simple and is accessible from blood donors.

T A B L E 2 Sociodemographic parameters in relation to seroprevalence of SARS-CoV-2 antibodies in the studied blood donors (total no. = 3058). In our survey, we found an increasing trend in prevalence throughout the study period: 13.2% during March (Group 1), 19.2%

during June (Group 2), and 66% during July (Group 3) (p < 0.001) ( Figure 1 ). Seropositive donors had humoral evidence of immunity against SARS-CoV-2.

Dynamics of the third peak in SARS CoV-19 in Egypt, according to WHO daily cases in Egypt, 13 are described in our study. We observed a peak of 66% seropositivity at the end of the wave. This dramatic rise was seen among healthy blood donors in parallel with widespread intracommunity transmission of the disease.

Our work reflects a high cumulative incidence of infection and seroconversion, which might be explained by the decline in infection rates in June. The decline in the spread of the virus went along with the high population seropositivity. A nadir in infection rates was observed by the end of July.

In this study, the antibody responses for SARS-CoV-2 were 34.43% (1053/3058 studied cases), which is higher than the previously published data that ranged from 1.6% to 4.1% among different populations. 8-10 These higher seropositive results may not entirely be representative of the general population in Egypt because the included blood donors were aged 18-59 years only with the exclusion of children and the elderly. Also, in this study, there was an increasing trend in the seropositive prevalence rates throughout the study period: 13.2% during March, 19.2% during June, and 66% during July (p < 0.001) (Figure 1 ). The WHO epidemic curve mirrors this trend, where the curve has been shown to be on the rise during March, April, and May, and then it started a downwards trend in June. The nadir was reached by the end of July. 13 Also, the low seropositivity during the period from March to June may be due to the method of detection of the qualitative nucleocapsid antibodies that disappear early (short-lived), resulting in low seroprevalence rates. [14] [15] [16] [17] On the other hand, the quantitative detection of the neutralizing antibodies is long-lived and probably demonstrates protection against further infection, particularly if the titer is high. 18 Another reason for the higher seroprevalence could be the change in the assay. Vaccinated individuals in Period 3 will have increased the seroprevalence detectable by the S assay. Since only 5% were vaccinated, it would not be inflated by more than that.

In this study, there was no significant correlation between seroprevalence and area of residence, Rhesus blood groups, or ABO 

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SARS-CoV-2 antibody seroprevalence rates among Egyptian blood donors around the third wave: cross-sectional study

We thank the Cairo University blood bank team for supporting the research team during data collection. This study was funded by Cairo University, COVID-19 Research Budget.

The authors declare no conflicts of interest.

This study was approved by the Research Ethics Committee, Faculty of Medicine, Cairo University on 14-5-2020 under the number: N-40-2020. Participants consented to participate in this study. The publication was foreseen in the acceptance of participation.

The manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and any discrepancies from the study as planned (and, irrelevant, registered) have been explained.

http://orcid.org/0000-0003-1822-5104