Control of Trachoma from Achham District, Nepal: A Cross-Sectional Study from the Nepal National Trachoma Program

Pant, Bidya Prasad; Bhatta, Ramesh; Chaudhary, J S P; Awasthi, Suresh; Mishra, Sailesh Kumar; Sharma, Shaveta; Cuddapah, Puja A.; Gwyn, Sarah; Stoller, Nicole E.; Martin, Diana L.; Keenan, Jeremy D.; Lietman, Thomas M.; Gaynor, Bruce D.

doi:10.1371/journal.pntd.0004462

Cited by 24 publications

(21 citation statements)

References 23 publications

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“…In a surveillance survey in two districts in Nepal, TF and infection were virtually absent and the low antibody seropositivity rate, average 2%, showed no increase with age among 1–9 year olds 10 . Similar findings from cross sectional studies in villages have also been reported 4 , 11 . The value for using serology as a surveillance tool is the potential ability to assess cumulative exposure to transmission of ocular C. trachomatis over the two year period between the final prevalence survey and the surveillance survey, plus the potential for integration with tests for antigens of other neglected tropical diseases.…”

Section: Introductionsupporting

confidence: 88%

Longitudinal change in the serology of antibodies to Chlamydia trachomatis pgp3 in children residing in a trachoma area

West

Muñoz

Kaur

et al. 2018

Sci Rep

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A serologic test for antibodies to chlamydial antigen pgp3 may be a useful tool for trachoma surveillance. However, little is known about the stability of antibody status over time, or factors associated with seroreversion/conversion. A cohort of 2,111 children ages 1–9 years in Tanzania were followed for one year in the absence of mass azithromycin. At baseline and follow-up, they were evaluated for trachoma, chlamydial infection, and antibodies to chlamydial antigen pgp3. At baseline, 31% of children were seropositive for pgp3 antibodies and 6.4% seroreverted to negative over one year. Of those seronegative, 9.8% seroconverted over the year. The seroreverters had lower baseline mean fluorescence intensity (MFI-BG) values compared to the seropositives who remained positive (Odds Ratio = 0.04 for every unit increase in log10MFI-BG, 95% CI = 0.02–0.09), and were more likely to live in communities with trachoma <5% (p < 0.008). While seroconversion was expected, seroreversion was unexpected. The low seroprevalence rate reported from low endemic areas may be due to seroreversion as well as lack of exposure.

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Section: Introductionsupporting

confidence: 88%

Longitudinal change in the serology of antibodies to Chlamydia trachomatis pgp3 in children residing in a trachoma area

West

Muñoz

Kaur

et al. 2018

Sci Rep

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“…In this sub-village, trachoma was 6·5%, whereas our trachoma rates were 3/1500 (0·2%). In a survey done as an impact assessment in Achham district in Nepal, low rates of infection and trachoma were also found, although too few children were tested for antibodies to determine a reliable rate of antibody positivity[ 16 ]. In the only other district surveillance prevalence survey, antibody prevalence in 30 communities in Kilosa district Tanzania was 7·5% and increased significantly with age from 5% in 1–3 year olds, to 9% in 7–9 year olds[ 9 ].…”

Section: Discussionmentioning

confidence: 99%

The World Health Organization Recommendations for Trachoma Surveillance, Experience in Nepal and Added Benefit of Testing for Antibodies to Chlamydia trachomatis pgp3 Protein: NESTS Study

Zambrano

Sharma²,

Crowley

et al. 2016

PLoS Negl Trop Dis

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BackgroundThe World Health Organization (WHO) now requires a second surveillance survey for trachoma after an impact assessment has found follicular trachoma (TF) <5% to determine if re-emergence has occurred. Using new WHO guidelines, we undertook surveillance surveys, and determined the prevalence of infection and antibody positivity, in two districts in Nepal.Methods20 clusters were randomly selected within each district, 15 were randomly selected for antibody testing. In each cluster, we randomly selected 50 children ages 1–9 years and 100 adults ≥15 years. TF and trachomatous trichiasis (TT) were evaluated. Conjunctival swabs to test for chlamydial infection using GenXpert platform were obtained, and dried blood spots were collected to test for antibodies to Chlamydia Trachomatis pgp3 using the Luminex platform.Findings3 cases of TF were found in the two districts, and one case of infection. Pgp3 antibody positivity was 2·4% (95% confidence interval: 1·4%, 3·7%), and did not increase with age (P = 0.24). No clustering of antibody positivity within communities was found. TT prevalence was <1/1,000 population.InterpretationThe surveillance surveys, as proposed by WHO, showed no evidence for re-emergence of trachoma in two districts of Nepal. The low level and no significant increase by age in seroprevalence of antibodies to C trachomatis pgp3 antigen deserve further investigation as a marker of interruption of transmission.

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“…Serology has recently been used in several studies [19,20,22–24], three of which have taken place in districts that have completed three or more rounds of MDA [22–24]. These studies have used the multiplex bead array platform (Bio-rad, Hercules, California) to detect antibodies against Pgp3 and CT694, antigens thought to be highly immunogenic [25].…”

Section: Introductionmentioning

confidence: 99%

“…To make serological testing more widely accessible, the Pgp3/CT694 assay used in previous studies [19,20,22–24] has been adapted for use in a simple Pgp3-specific enzyme-linked immunosorbent assay (ELISA). Pgp3 is a Ct-specific 84kDa heterotrimeric protein [27] and is recognised by specific IgG [28].…”

Section: Introductionmentioning

confidence: 99%

Defining Seropositivity Thresholds for Use in Trachoma Elimination Studies

et al. 2017

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BackgroundEfforts are underway to eliminate trachoma as a public health problem by 2020. Programmatic guidelines are based on clinical signs that correlate poorly with Chlamydia trachomatis (Ct) infection in post-treatment and low-endemicity settings. Age-specific seroprevalence of anti Ct Pgp3 antibodies has been proposed as an alternative indicator of the need for intervention. To standardise the use of these tools, it is necessary to develop an analytical approach that performs reproducibly both within and between studies.MethodologyDried blood spots were collected in 2014 from children aged 1–9 years in Laos (n = 952) and Uganda (n = 2700) and from people aged 1–90 years in The Gambia (n = 1868). Anti-Pgp3 antibodies were detected by ELISA. A number of visual and statistical analytical approaches for defining serological status were compared.Principal FindingsSeroprevalence was estimated at 11.3% (Laos), 13.4% (Uganda) and 29.3% (The Gambia) by visual inspection of the inflection point. The expectation-maximisation algorithm estimated seroprevalence at 10.4% (Laos), 24.3% (Uganda) and 29.3% (The Gambia). Finite mixture model estimates were 15.6% (Laos), 17.1% (Uganda) and 26.2% (The Gambia). Receiver operating characteristic (ROC) curve analysis using a threshold calibrated against external reference specimens estimated the seroprevalence at 6.7% (Laos), 6.8% (Uganda) and 20.9% (The Gambia) when the threshold was set to optimise Youden’s J index. The ROC curve analysis was found to estimate seroprevalence at lower levels than estimates based on thresholds established using internal reference data. Thresholds defined using internal reference threshold methods did not vary substantially between population samples.ConclusionsInternally calibrated approaches to threshold specification are reproducible and consistent and thus have advantages over methods that require external calibrators. We propose that future serological analyses in trachoma use a finite mixture model or expectation-maximisation algorithm as a means of setting the threshold for ELISA data. This will facilitate standardisation and harmonisation between studies and eliminate the need to establish and maintain a global calibration standard.

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Control of Trachoma from Achham District, Nepal: A Cross-Sectional Study from the Nepal National Trachoma Program

Cited by 24 publications

References 23 publications

Longitudinal change in the serology of antibodies to Chlamydia trachomatis pgp3 in children residing in a trachoma area

Longitudinal change in the serology of antibodies to Chlamydia trachomatis pgp3 in children residing in a trachoma area

The World Health Organization Recommendations for Trachoma Surveillance, Experience in Nepal and Added Benefit of Testing for Antibodies to Chlamydia trachomatis pgp3 Protein: NESTS Study

Defining Seropositivity Thresholds for Use in Trachoma Elimination Studies

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