Statistical analysis

The apparent seroprevalence was computed as the proportion of individuals with a reactive result in the IgM or IgG band. We compared groups using the Pearson Χ² or the Fisher’s exact test, when the assumptions for the Χ² test did not hold. To measure the association of participants’ characteristics and IgM, IgG, and IgM or IgG seroprevalence, we computed the odds ratios (OR) and 95% CI adjusted for age, gender, educational level and nationality (except the occupational group that was not adjusted for education) using a logistic regression in SPSS V.27.

We estimated the true prevalence and 95% credible intervals (95% CrI) using Bayesian inference, considering a uniform prior distribution for sensitivity ranging from 0.65 to 0.97, and specificity between 0.83 and 1, as described by Speybroeck et al.¹⁰ Estimates were obtained using the ‘prevalence’ and ‘rjags’ package in R.¹¹