Normalized optical density (in an ELISA for anti-Pgp3 antibody) in sera from 1–9-year-old children who were positive (red spots in panel (a)) and negative (blue spots in panel (a)) for conjunctival <i>Chlamydia trachomatis</i> infection by droplet digital PCR, Kiritimati Island, Kiribati, November 2015.

<p>In panel (a), the threshold for anti-Pgp3 seropositivity, derived using a finite mixture model, is indicated (dotted line), and within each one-year age band, spots have been moved horizontally in order to separate data points that would otherwise have been superimposed. In panel (b), red lines represent the median values, grey boxes represent inter-quartile ranges, whiskers represent the minima and maxima.</p

Infection with <i>Chlamydia trachomatis</i> in 1–9-year-old children, with and without active trachoma in either eye, Kiritimati Island, Kiribati, November 2015.

<p>TF = trachomatous inflammation—follicular; TI = trachomatous inflammation—intense; ddPCR = droplet digital polymerase chain reaction.</p

Age-specific prevalence of anti-Pgp3 antibodies in 1–9-year-old children, Kiritimati Island, Kiribati, November 2015.

<p>Grey columns indicate the seroprevalence estimate for each one-year age band; red lines indicate 95% confidence intervals around those estimates.</p

Normalized optical density (in an ELISA for anti-Pgp3 antibody) in sera from 1–9-year-old children with and without active trachoma in either eye, Kiritimati Island, Kiribati, November 2015.

<p>Red lines represent the median value, grey boxes represent inter-quartile range and whiskers represent the minima and maxima.</p

Reactivity to Pgp3 in 1–9-year-old children with and without active trachoma in either eye, Kiritimati Island, Kiribati, November 2015.

<p>TF = trachomatous inflammation—follicular; TI = trachomatous inflammation—intense.</p

Load of <i>Chlamydia trachomatis</i> infection in 1–9-year-old children with and without active trachoma in either eye, Kiritimati Island, Kiribati, November 2015.

<p>Red lines represent the median value, grey boxes represent inter-quartile ranges and whiskers represent the minima and maxima. TF = trachomatous inflammation—follicular; TI = trachomatous inflammation—intense.</p

Normalized optical density (in an ELISA for anti-Pgp3 antibody) in sera from 1–9-year-old children who were positive (red spots in panel (a)) and negative (blue spots in panel (a)) for conjunctival <i>Chlamydia trachomatis</i> infection by droplet digital PCR, Kiritimati Island, Kiribati, November 2015.

<p>In panel (a), the threshold for anti-Pgp3 seropositivity, derived using a finite mixture model, is indicated (dotted line), and within each one-year age band, spots have been moved horizontally in order to separate data points that would otherwise have been superimposed. In panel (b), red lines represent the median values, grey boxes represent inter-quartile ranges, whiskers represent the minima and maxima.</p

Map of Kiribati, with zoomed maps of Tarawa (lower left panel) and Kiritimati (lower right panel).

<p>Produced in Miller projection using QGIS 2.16. Shapefiles from gadm.org.</p

Tropical Data: Approach and Methodology as Applied to Trachoma Prevalence Surveys

Population-based prevalence surveys are essential for decision-making on interventions to achieve trachoma elimination as a public health problem. This paper outlines the methodologies of Tropical Data, which supports work to undertake those surveys. Tropical Data is a consortium of partners that supports health ministries worldwide to conduct globally standardised prevalence surveys that conform to World Health Organization recommendations. Founding principles are health ministry ownership, partnership and collaboration, and quality assurance and quality control at every step of the survey process. Support covers survey planning, survey design, training, electronic data collection and fieldwork, and data management, analysis and dissemination. Methods are adapted to meet local context and needs. Customisations, operational research and integration of other diseases into routine trachoma surveys have also been supported. Between 29th February 2016 and 24th April 2023, 3373 trachoma surveys across 50 countries have been supported, resulting in 10,818,502 people being examined for trachoma. This health ministry-led, standardised approach, with support from the start to the end of the survey process, has helped all trachoma elimination stakeholders to know where interventions are needed, where interventions can be stopped, and when elimination as a public health problem has been achieved. Flexibility to meet specific country contexts, adaptation to changes in global guidance and adjustments in response to user feedback have facilitated innovation in evidence-based methodologies, and supported health ministries to strive for global disease control targets.</p