Abstract
Abstract
Serology is increasingly used to monitor infection transmission and disease elimination. Embedding dried blood spot collection in trachoma surveys allows transmission intensity inference through population-level seroconversion rate (SCR) estimation, but no formal assessment of required sample size has been published. Using serology data from 40 trachoma prevalence surveys, we estimated seroprevalence intra-cluster correlation coefficient, a key design parameter, and assessed survey design considerations for incorporating serological monitoring. Design scenarios focused on proposed operational SCR thresholds (2.2 [no action needed] and 4.5 [action needed] per 100 child years) for interpretation of serological data in low-transmission and post-elimination settings. We evaluated SCR estimation in 42 two-stage designs by calculating precision (confidence interval width around an SCR value) and power (the measure of deviation of suggested thresholds to the SCR value). When the SCR is ≤1.5 and >5.7 per 100 person-years, sample sizes between 300-2000 allowed good precision of SCR estimation. We anticipate a standard prevalence survey with 30 clusters and 30 households per cluster should provide ≥80% power to determine that an SCR ≤1.2 falls below a 2.2 threshold and SCR ≥5.7 falls above a 4.5 threshold. Our results support collection of serological data via the recommended survey design for trachoma surveillance.