Prevalence of signs of trachoma, ocular Chlamydia trachomatis infection and antibodies to Pgp3 in residents of Kiritimati Island, Kiribati.

OBJECTIVE: In some Pacific Island countries, such as Solomon Islands and Fiji, active trachoma is common, but ocular Chlamydia trachomatis (Ct) infection and trachomatous trichiasis (TT) are rare. On Tarawa, the most populous Kiribati island, both the active trachoma sign "trachomatous inflammation-follicular" (TF) and TT are present at prevalences warranting intervention. We sought to estimate prevalences of TF, TT, ocular Ct infection, and anti-Ct antibodies on Kiritimati Island, Kiribati, to assess local relationships between these parameters, and to help determine the need for interventions against trachoma on Kiribati islands other than Tarawa. METHODS: As part of the Global Trachoma Mapping Project (GTMP), on Kiritimati, we examined 406 children aged 1-9 years for active trachoma. We collected conjunctival swabs (for droplet digital PCR against Ct plasmid targets) from 1-9-year-olds with active trachoma, and a systematic selection of 1-9-year-olds without active trachoma. We collected dried blood spots (for anti-Pgp3 ELISA) from all 1-9-year-old children. We also examined 416 adults aged ≥15 years for TT. Prevalence of TF and TT was adjusted for age (TF) or age and gender (TT) in five-year age bands. RESULTS: The age-adjusted prevalence of TF in 1-9-year-olds was 28% (95% confidence interval [CI]: 24-35). The age- and gender-adjusted prevalence of TT in those aged ≥15 years was 0.2% (95% CI: 0.1-0.3%). Twenty-six (13.5%) of 193 swabs from children without active trachoma, and 58 (49.2%) of 118 swabs from children with active trachoma were positive for Ct DNA. Two hundred and ten (53%) of 397 children had anti-Pgp3 antibodies. Both infection (p<0.0001) and seropositivity (p<0.0001) were strongly associated with active trachoma. In 1-9-year-olds, the prevalence of anti-Pgp3 antibodies rose steeply with age. CONCLUSION: Trachoma presents a public health problem on Kiritimati, where the high prevalence of ocular Ct infection and rapid increase in seropositivity with age suggest intense Ct transmission amongst young children. Interventions are required here to prevent future blindness

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

PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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

The utility of serology for elimination surveillance of trachoma.

Robust surveillance methods are needed for trachoma control and recrudescence monitoring, but existing methods have limitations. Here, we analyse data from nine trachoma-endemic populations and provide operational thresholds for interpretation of serological data in low-transmission and post-elimination settings. Analyses with sero-catalytic and antibody acquisition models provide insights into transmission history within each population. To accurately estimate sero-conversion rates (SCR) for trachoma in populations with high-seroprevalence in adults, the model accounts for secondary exposure to Chlamydia trachomatis due to urogenital infection. We estimate the population half-life of sero-reversion for anti-Pgp3 antibodies to be 26 (95% credible interval (CrI): 21-34) years. We show SCRs below 0.015 (95% confidence interval (CI): 0.0-0.049) per year correspond to a prevalence of trachomatous inflammation-follicular below 5%, the current threshold for elimination of active trachoma as a public health problem. As global trachoma prevalence declines, we may need cross-sectional serological survey data to inform programmatic decisions

The utility of serology for elimination surveillance of trachoma

Robust surveillance methods are needed for trachoma control and recrudescence monitoring, but existing methods have limitations. Here, Pinsent et al. analyse data from nine trachoma-endemic populations and provide operational thresholds for interpretation of serological data in low transmission and post-elimination settings

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

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