• Waleed H Mahallawi, Mohammad A Alsarani, Rami H Aljohani, Abdulrahman A Alluhaibi, Turki H Alamri, Nadir A Ibrahim, Khalid H Mahallawi, and Omar F Khabourd.
• From the Medical Laboratory Technology Department, College of Applied Medical Sciences, Taibah University, Madinah, Saudi Arabia.
• Ann Saudi Med. 2022 Mar 1; 42 (2): 69-74.

BackgroundThe coronavirus disease 2019 (COVID-19) pandemic has had a massive impact on public health as well as the economy. Understanding the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection among undiagnosed individuals is important for developing an informed pandemic response.ObjectiveInvestigate the prevalence of undiagnosed COVID-19 disease.DesignCross-sectional.SettingTertiary care center in Madinah, Saudi Arabia.Subjects And MethodsAll participants were on follow-up visits to various clinics and had not been previously diagnosed with COVID-19. Enzyme-linked immunosorbent assay was used to specifically assess the anti-spike IgG antibody seropositivity in serum samples. We associated the seropositivity rates of the participants with age, body mass index (BMI), nationality, blood groups, and sex with uni- and multivariate analyses.Main Outcome MeasuresSeropositivity for IgG anti-spike antibodies against SARS-CoV-2.Sample Size And Characteristics527 subjects, with a median (interquartile percentiles) age of the 527 subjects was 34 (24-41).ResultsOf the 527 samples, about one-fourth (n=124, 23.5%) were positive for anti-spike IgG antibody against SARS CoV-2. Age was associated with anti-spike IgG antibody positivity (P<.002). Participants >30 years were more likely to be seropositive (28-29%) than younger participants (15.4%). Additionally, seropositivity was associated with female gender (P<.001) and a higher BMI (P<.006). In the multivariate logistic regression, age >30, female gender and BMI >40 were associated with seropositivity.ConclusionThe percentage of seropositive individuals reflects the high level of undiagnosed COVID-19 patients among the population. Our results will help in a better evaluation of the public health measures applied during the COVID-19 pandemic and any future public health crises.LimitationsSample size was small, single-center study and no rural areas were included.Conflict Of InterestNone.

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