Seroprevalence of SARS-CoV-2 Infection in Portugal in May-July 2020: Results of the First National Serological Survey (ISNCOVID-19)

Authors

  • Irina Kislaya Departamento de Epidemiologia. Instituto Nacional de Saúde Doutor Ricardo Jorge. Lisboa. https://orcid.org/0000-0001-5772-2416
  • Paulo Gonçalves Departamento de Doenças Infeciosas. Instituto Nacional de Saúde Doutor Ricardo Jorge. Lisboa.
  • Marta Barreto Departamento de Epidemiologia. Instituto Nacional de Saúde Doutor Ricardo Jorge. Lisboa.
  • Rita de Sousa Departamento de Doenças Infeciosas. Instituto Nacional de Saúde Doutor Ricardo Jorge. Lisboa.
  • Ana Cristina Garcia Departamento de Epidemiologia. Instituto Nacional de Saúde Doutor Ricardo Jorge. Lisboa.
  • Rita Matos Departamento de Doenças Infeciosas. Instituto Nacional de Saúde Doutor Ricardo Jorge. Lisboa.
  • Raquel Guiomar Departamento de Doenças Infeciosas. Instituto Nacional de Saúde Doutor Ricardo Jorge. Lisboa.
  • Ana Paula Rodrigues Departamento de Epidemiologia. Instituto Nacional de Saúde Doutor Ricardo Jorge. Lisboa.
  • On behalf of ISNCOVID-19 Group

DOI:

https://doi.org/10.20344/amp.15122

Keywords:

Antibodies, Viral, COVID-19, COVID-19 Testing, Immunoglobulin G, Immunoglobulin M, Portugal, SARS-CoV-2, Seroepidemiologic Studies

Abstract

Introduction: The aim of this study was to estimate and describe the prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific antibodies (immunoglobulin M and/or immunoglobulin G) in Portugal in May-July 2020.
Material and Methods: A cross-sectional seroepidemiological survey was developed after the peak of the first epidemic wave on a sample of 2301 Portuguese residents, aged 1 year or older. Survey sample was selected using a two-stage stratified non-probability sampling design (quota sampling). SARS-CoV-2 immunoglobulin M and immunoglobulin G antibodies were measured in serum samples by enzyme-linked immunosorbent assay. Seroprevalence estimates of immunoglobulin M and/or immunoglobulin G and 95% confidence intervals were stratified by sex, age group, health region and education.
Results: Overall, seroprevalence was 2.9% (95% confidence interval: 2.0% - 4.2%). Higher prevalence rates were observed in male (4.1%, 95% confidence interval: 2.6% - 6.6%) and those with secondary education (6.4%, 95% confidence interval: 3.2% - 12.5%). Differences in seroprevalence by age group and region were not statistically significant.
Discussion: The estimated seroprevalence of SARS-CoV-2 was higher than the cumulative incidence reported by the National Surveillance System but far from necessary to reach herd immunity.
Conclusion: Our results support limited extent of infection by SARS-CoV-2 in the study population possibly due to early lockdown measures implemented in Portugal and support the need to continue monitoring of SARS-CoV-2 seroprevalence in order to increase our knowledge about the evolution of the epidemic and to estimate the proportion of the susceptible population over time.

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Author Biography

Irina Kislaya, Departamento de Epidemiologia. Instituto Nacional de Saúde Doutor Ricardo Jorge. Lisboa.

Técnica Superior, Departamento de Epidemiologia, Instituto Nacional de Saúde Doutor Ricardo Jorge

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Published

2021-02-01

How to Cite

1.
Kislaya I, Gonçalves P, Barreto M, de Sousa R, Garcia AC, Matos R, Guiomar R, Rodrigues AP, ISNCOVID-19 Group O behalf of. Seroprevalence of SARS-CoV-2 Infection in Portugal in May-July 2020: Results of the First National Serological Survey (ISNCOVID-19). Acta Med Port [Internet]. 2021 Feb. 1 [cited 2023 Feb. 6];34(2):87-94. Available from: https://actamedicaportuguesa.com/revista/index.php/amp/article/view/15122

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Original