Author/Editor		Poljak, Mario; Oštrbenk Valenčak, Anja; Štrumbelj, Erik; Maver Vodičar, Polona; Vehovar, Vasja; Resman Rus, Katarina; Korva, Miša; Knap, Nataša; Seme, Katja; Petrovec, Miroslav; Zupan, Blaž; Demšar, Janez; Kurdija, Slavko; Avšič-Županc, Tatjana
Title		Seroprevalence of severe acute respiratory syndrome coronavirus 2 in Slovenia
Type		članek
Publication year		2021
Volume		str. str.
ISSN		1198-743X - Clinical microbiology and infection : the official publication of the European Society of Clinical Microbiology and Infectious Diseases
Language		eng
Abstract		Objectives: Seroprevalence surveys provide crucial information on cumulative severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exposure. This Slovenian nationwide population study is the first longitudinal 6-month serosurvey using probability-based samples across all age categories. Methods: Each participant supplied two blood samples: 1316 samples in April 2020 (first round) and 1211 in October/November 2020 (second round). The first-round sera were tested using Euroimmun Anti-SARS-CoV-2 ELISA IgG (ELISA) and, because of uncertain estimates, were retested using Elecsys Anti-SARS-CoV-2 (Elecsys-N) and Elecsys Anti-SARS-CoV-2 S (Elecsys-S). The second-round sera were concomitantly tested using Elecsys-N/Elecsys-S. Results: The populations of both rounds matched the overall population (n = 3000), with minor settlement type and age differences. The first-round seroprevalence corrected for the ELISA manufacturer's specificity was 2.78% (95% highest density interval [HDI] 1.81%-3.80%), corrected using pooled ELISA specificity calculated from published data 0.93% (95% CI 0.00%-2.65%), and based on Elecsys-N/Elecsys-S results 0.87% (95% HDI 0.40%-1.38%). The second-round unadjusted lower limit of seroprevalence on 11 November 2020 was 4.06% (95% HDI 2.97%-5.16%) and on 3 October 2020, unadjusted upper limit was 4.29% (95% HDI 3.18%-5.47%). Conclusions: SARS-CoV-2 seroprevalence in Slovenia increased four-fold from late April to October/November 2020, mainly due to a devastating second wave. Significant logistic/methodological challenges accompanied both rounds. The main lessons learned were a need for caution when relying on manufacturer-generated assay evaluation data, the importance of multiple manufacturer-independent assay performance assessments, the need for concomitant use of highly-specific serological assays targeting different SARS-CoV-2 proteins in serosurveys conducted in low-prevalence settings or during epidemic exponential growth and the usefulness of a Bayesian approach for overcoming complex methodological challenges.
Keywords		coronavirus disease 2019 probability-based sample severe acute respiratory syndrome koronavirusna bolezen 2019 vzorec na podlagi verjetnosti hud akutni respiratorni sindrom