<p>Correct identification of reason for presenting symptoms, overall and by case variant. Variant-level analyses are exploratory and p-values are unadjusted. Round-specific p-values compare study arms within a round using chi-square tests. Difference-in-differences p-values test the arm-by-time interaction from the regression model.</p>

Correct identification of reason for presenting symptoms, overall and by case variant. Variant-level analyses are exploratory and p-values are unadjusted. Round-specific p-values compare study arms within a round using chi-square tests. Difference-in-differences p-values test the arm-by-time interaction from the regression model.