Modelling lymphatic filariasis elimination in American Samoa: GEOFIL predicts need for new targets and six rounds of mass drug administration

McLure, Angus; Graves, Patricia M.; Lau, Colleen L; Shaw, Callum; Glass, Kathryn M.

doi:10.1016/j.epidem.2022.100591

Cited by 6 publications

(7 citation statements)

References 36 publications

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“…To achieve the desired household and village mf intra-cluster correlations in GEOFIL, we found there had to be, on average, more transmission during off-work hours than during working hours. This unequal distribution in the timing of infection shifted the location where transmission was dominant, and caused an increase in transmission at the household and a decrease in transmission at schools and workplaces compared to previous versions of GEOFIL [ 21 ]. Further details on the results of the ABC fitting are given in S1 Fig .…”

Section: Resultsmentioning

confidence: 99%

“…As appropriately modelling the clustering of LF cases was key to assessing the effectiveness of targeted strategies, we refitted the previous GEOFIL model [ 21 ] to reproduce the degree of clustering at the household and village level observed in a previous 2016 community survey [ 37 ]. As we only had intra-cluster correlation (ICC) values for microfilariae (mf) positivity from the 2016 survey, the model was initialised in 2010 with prevalence data from a 2010 community survey [ 35 ], but with village and household level mf ICC values from the 2016 survey.…”

Section: Methodsmentioning

confidence: 99%

“…American Samoa subsequently implemented two rounds of 3D-MDA in 2018 and 2019; however, a 2019 community survey found transmission was still ongoing [ 20 ]. There was a further round of 3D-MDA in 2021, but it is unclear if this additional round will be enough to ensure long-term LF elimination [ 21 ].…”

Section: Introductionmentioning

confidence: 99%

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Lymphatic filariasis endgame strategies: Using GEOFIL to model mass drug administration and targeted surveillance and treatment strategies in American Samoa

et al. 2023

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American Samoa underwent seven rounds of mass drug administration (MDA) for lymphatic filariasis (LF) from 2000-2006, but subsequent surveys found evidence of ongoing transmission. American Samoa has since undergone further rounds of MDA in 2018, 2019, and 2021; however, recent surveys indicate that transmission is still ongoing. GEOFIL, a spatially-explicit agent-based LF model, was used to compare the effectiveness of territory-wide triple-drug MDA (3D-MDA) with targeted surveillance and treatment strategies. Both approaches relied on treatment with ivermectin, diethylcarbamazine, and albendazole. We simulated three levels of whole population coverage for 3D-MDA: 65%, 73%, and 85%, while the targeted strategies relied on surveillance in schools, workplaces, and households, followed by targeted treatment. In the household-based strategies, we simulated 1-5 teams travelling village-to-village and offering antigen (Ag) testing to randomly selected households in each village. If an Ag-positive person was identified, treatment was offered to members of all households within 100m-1km of the positive case. All simulated interventions were finished by 2027 and their effectiveness was judged by their ‘control probability’—the proportion of simulations in which microfilariae prevalence decreased between 2030 and 2035. Without future intervention, we predict Ag prevalence will rebound. With 3D-MDA, a 90% control probability required an estimated ≥ 4 further rounds with 65% coverage, ≥ 3 rounds with 73% coverage, or ≥ 2 rounds with 85% coverage. While household-based strategies were substantially more testing-intensive than 3D-MDA, they could offer comparable control probabilities with substantially fewer treatments; e.g. three teams aiming to test 50% of households and offering treatment to a 500m radius had approximately the same control probability as three rounds of 73% 3D-MDA, but used < 40% the number of treatments. School- and workplace-based interventions proved ineffective. Regardless of strategy, reducing Ag prevalence below the 1% target threshold recommended by the World Health Organization was a poor indicator of the interruption of LF transmission, highlighting the need to review blanket elimination targets.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Lymphatic filariasis endgame strategies: Using GEOFIL to model mass drug administration and targeted surveillance and treatment strategies in American Samoa

et al. 2023

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“…The GPS locations of the surveyed households were used to delineate a buffer zone of 20 m around the households in ArcGIS [ 41 ]. The buffer size was selected to represent an approximate distance within which the participants would spend extensive periods of time, and therefore have greatest exposure to the environmental conditions within the buffers [ 42 ]. For each surveyed location, the data extracted within the buffer zone included the spatial mean values of population density, distance to coastline and streams, elevation, annual average rainfall, rainfall in the wettest (December) and driest (August) months in 2016, annual average temperature, and temperature of hottest (January) and coolest (July) months in the same year.…”

Section: Methodsmentioning

confidence: 99%

Spatial predictive risk mapping of lymphatic filariasis residual hotspots in American Samoa using demographic and environmental factors

Restrepo¹,

Martin²,

Fuimaono³

et al. 2023

PLoS Negl Trop Dis

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Background American Samoa successfully completed seven rounds of mass drug administration (MDA) for lymphatic filariasis (LF) from 2000–2006. The territory passed the school-based transmission assessment surveys in 2011 and 2015 but failed in 2016. One of the key challenges after the implementation of MDA is the identification of any residual hotspots of transmission. Method Based on data collected in a 2016 community survey in persons aged ≥8 years, Bayesian geostatistical models were developed for LF antigen (Ag), and Wb123, Bm14, Bm33 antibodies (Abs) to predict spatial variation in infection markers using demographic and environmental factors (including land cover, elevation, rainfall, distance to the coastline and distance to streams). Results In the Ag model, females had a 26.8% (95% CrI: 11.0–39.8%) lower risk of being Ag-positive than males. There was a 2.4% (95% CrI: 1.8–3.0%) increase in the odds of Ag positivity for every year of age. Also, the odds of Ag-positivity increased by 0.4% (95% CrI: 0.1–0.7%) for each 1% increase in tree cover. The models for Wb123, Bm14 and Bm33 Abs showed similar significant associations as the Ag model for sex, age and tree coverage. After accounting for the effect of covariates, the radii of the clusters were larger for Bm14 and Bm33 Abs compared to Ag and Wb123 Ab. The predictive maps showed that Ab-positivity was more widespread across the territory, while Ag-positivity was more confined to villages in the north-west of the main island. Conclusion The findings may facilitate more specific targeting of post-MDA surveillance activities by prioritising those areas at higher risk of ongoing transmission.

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“…The GPS locations of the surveyed households were used to delineate a buffer zone of 20 m around the households in ArcGIS (39). The buffer size was selected to represent an approximate distance within which the participants would spend extensive periods of time, and therefore have greatest exposure to the environmental conditions withing the buffers (40). For each surveyed location, the data extracted within the buffer zone included the spatial mean values of population density, distance to coastline and streams, elevation, annual average rainfall, rainfall in the wettest (December) and driest (August) months in 2016, annual average temperature, and temperature of hottest (January) and coolest (July) months in the same year.…”

Section: Methodsmentioning

confidence: 99%

Predictive risk mapping of lymphatic filariasis residual hotspots in American Samoa using demographic and environmental factors

Restrepo

Martin

Fuimaono

et al. 2022

Preprint

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BackgroundAmerican Samoa successfully completed seven rounds of mass drug administration (MDA) for lymphatic filariasis (LF) from 2000-2006. The territory passed the school-based transmission assessment surveys in 2011 and 2015 but failed in 2016. One of the key challenges after the implementation of MDA is the identification of any residual hotspots of transmission. MethodBased on data collected in a 2016 community survey in persons aged >=8 years, Bayesian geostatistical models were developed for LF antigen (Ag), and Wb123, Bm14, Bm33 antibodies (Abs) to predict spatial variation in infection markers using demographic and environmental factors (including land cover, elevation, rainfall, distance to the coastline and distance to streams). ResultsIn the Ag model, females had a 29.6% (95% CrI: 16.0–41.1%) lower risk of being Ag-positive than males. There was a 1.4% (95% CrI: 0.02–2.7%) increase in the odds of Ag positivity for every year of age. Also, the odds of Ag-positivity increased by 0.6% (95% CrI: 0.06–0.61%) for each 1% increase in tree cover. The models for Wb123, Bm14 and Bm33 Abs showed similar significant associations as the Ag model for sex, age and tree coverage. After accounting for the effect of covariates, the radii of the clusters were larger for Bm14 and Bm33 Abs compared to Ag and Wb123 Ab. The predictive maps showed that Ab-positivity was more widespread across the territory, while Ag-positivity was more confined to villages in the north-west of the main island. ConclusionThe findings may facilitate more specific targeting of post-MDA surveillance activities by prioritising those areas at higher risk of ongoing transmission.

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Modelling lymphatic filariasis elimination in American Samoa: GEOFIL predicts need for new targets and six rounds of mass drug administration

Cited by 6 publications

References 36 publications

Lymphatic filariasis endgame strategies: Using GEOFIL to model mass drug administration and targeted surveillance and treatment strategies in American Samoa

Lymphatic filariasis endgame strategies: Using GEOFIL to model mass drug administration and targeted surveillance and treatment strategies in American Samoa

Spatial predictive risk mapping of lymphatic filariasis residual hotspots in American Samoa using demographic and environmental factors

Predictive risk mapping of lymphatic filariasis residual hotspots in American Samoa using demographic and environmental factors

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