Publication date: Feb 18, 2025

The seroprevalence of SARS-CoV-2 infection may be assessed using serologic tests to determine the presence of specific antibodies. This study evaluated the prevalence of SARS-CoV-2 nucleocapsid antibodies and the potential risk factors associated to seroprevalence in adult outpatients from Western Romania. We investigated 2089 consecutive adult outpatients for the presence of SARS-CoV-2 nucleocapsid antibodies, by using the Elecsys anti-SARS-CoV-2 electrochemiluminescence immunoassay. Study participants were residents of Timis County, Western Romania, who presented for routine laboratory investigations at the Municipal and County Clinical Emergency Hospitals Outpatient Clinics between 17 January 2023 - 14 March 2023. Participants completed an epidemiological questionnaire, including their medical history. The overall SARS-CoV-2 seroprevalence was 88. 37% (1846/2089) and was not significantly associated with gender and area of residence. Of 1846 study participants with detectable SARS-CoV-2 antibodies, 904 (48. 97%) reported no SARS-CoV-2 infection before the collection date, indicating that these individuals didn’t know that they were previously infected. Of the 992 adult outpatients with history of COVID-19, 50 (5. 04%) had no detectable SARS-CoV-2 nucleocapsid antibodies. Results of the serologic tests and responses to the questionnaire revealed that 1896 (90. 76%) of the 2089 participants were infected with SARS-CoV-2. The multivariate logistic regression analysis revealed that SARS-CoV-2 seroprevalence was associated with age, associated cancer disease, smoking status, number of COVID-19 vaccine doses received and number of previously diagnosed SARS-CoV-2 infections. Overall, no significant difference in SARS-CoV-2 seroprevalence was observed between healthy participants (89. 23%, 853/956) compared to adult outpatients with associated chronic diseases (87. 64%, 993/1133) (p = 0. 26). This study provides evidence of the high prevalence of SARS-CoV-2 infection. After three years of COVID-19 pandemic, 9 in 10 Romanian adults were previously infected, before or after vaccination, with the highest rates of infection in unvaccinated individuals and the lowest among vaccinated persons with a booster. Our results confirm that vaccination remains a highly effective measure to prevent SARS-CoV-2 infection.

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