Seroconversion Rate for Post-Validation Surveillance of Trachoma Open Access

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

About this Master's Thesis

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School	Rollins School of Public Health
Department	Environmental Health
Degree	M.P.H.
Submission	Master's Thesis
Language	English
Research Field	Health Sciences, Immunology Health Sciences, Epidemiology Health Sciences, Public Health
Keyword	seroconversion rate seroprevalence trachoma multiplex assay antibody response lateral flow assay
Committee Chair / Thesis Advisor	Weiss, Paul, Emory University
Committee Members	Freeman, Matthew, Emory University Martin, Diana, Centers for Disease Control and Prevention
Partnering Agencies	CDC

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