Seroconversion Rate for Post-Validation Surveillance of Trachoma Open Access

Randall, Jessica (Spring 2019)

Permanent URL: https://etd.library.emory.edu/concern/etds/8w32r672x?locale=en
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Abstract

Purpose: The WHO  is considering the utility of serological surveillance for trachoma. If comparable to clinical diagnoses, this type of surveillance would be a cost-effective and sustainable solution. Our serological survey from two districts in The Republic of Togo, a country now known to have reached the threshold for elimination of trachoma as a public health problem, supports the use of a seroconversion rate as an estimate of force of infection in non-endemic areas.

Methods: We conducted serological surveillance on 2915 participants 1-9 years old in two districts purposefully selected as the most likely to have trachoma if it would be in the country at all. Each participant had a finger-prick blood sample collected onto filter paper. We fit a logistic regression model to estimate seroprevalence. Participants had blood collected to measure antibody responses to the C. trachomatis (CT) antigens Pgp3 and Ct694 by multiplex bead-based immunoassay (MBA), the lab-based dipstick Pgp3 lateral flow assay (LFA), and the field based cassette Pgp3 lateral flow assay.We calculated a seroconversion rate for each antigen by fitting a reversible serocatalytic model which assumes zero seroreversion. We report median fluorescence intensity-background (MFI-BG ), seroprevalence, age-specific seroprevalence and seroconversion rate.

Results: Out of 2915 samples, 96% were negative by the MBA and LFA. Age-specific seroprevalence was estimated using a logistic regression model. Mean SCRs for each antigen and assay method were estimated by taking the mean of each age-specific seroconversion rate.

Conclusions: Our results support those of a parent study that found that the clinical diagnosis of trachoma, trachomatous inflammation- follicular (TF) falls below the 5% WHO threshold of elimination of trachoma as a public health problem. Our calculation of a seroconversion rate, an estimation of the force of infection, indicated no active transmission.

Table of Contents

Introduction: ........................................................................................................................1

Methods: ..............................................................................................................................3

Results: ................................................................................................................................6

Discussion: ...........................................................................................................................8

Conclusions and Recommendations: ..................................................................................... 10

References: ..........................................................................................................................11

Tables and Figures: ...............................................................................................................13

Appendix…………………………………………………………………….…………...................................15

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