Abstract
As the prevalence of lymphatic filariasis declines, it becomes crucial to adequately eliminate residual areas of endemicity and implement surveillance. To this end, serological assays have been developed, including the Bm14 Filariasis CELISA which recommends a specific optical density cut-off level. We used mixture modelling to assess positive cut-offs of Bm14 serology in children in Vanuatu using historical OD (Optical Density) ELISA values collected from a transmission assessment survey (2005) and a targeted child survey (2008). Mixture modelling is a statistical technique using probability distributions to identify subpopulations of positive and negative results (absolute cut-off value) and an 80% indeterminate range around the absolute cut-off (80% cut-off). Depending on programmatic choices, utilizing the lower 80% cut-off ensures the inclusion of all likely positives, however with the trade-off of lower specificity. For 2005, country-wide antibody prevalence estimates varied from 6.4% (previous cut-off) through 9.0% (absolute cut-off) to 17.3% (lower 80% cut-off). This corroborated historical evidence of hotspots in Pentecost Island in Penama province. For 2008, there were no differences in the prevalence rates using any of the thresholds. In conclusion, mixture modelling is a powerful tool that allows closer monitoring of residual transmission spots and these findings supported additional monitoring which was conducted in Penama in later years. Utilizing a statistical data-based cut-off, as opposed to a universal cut-off, may help guide program decisions that are better suited to the national program.
Highlights
Lymphatic filariasis (LF) is one of the world’s leading causes of disability [1]
The lymphatic filariasis (LF) program is reaching a crucial turning point whereby it has become critical to employ diagnostic tools that are capable of reliably informing programmatic decisions concerning the cessation of mass drug administrations (MDAs) and, subsequently, the validation of the elimination of LF as a public health problem
Given the difficulty of very low prevalence in young children and large sample sizes needed to detect low antigen prevalence in the endgame, the current focus is shifting towards considering antibody serology as a tool in these end-stages
Summary
Lymphatic filariasis (LF) is one of the world’s leading causes of disability [1]. This debilitating vector-borne disease, caused by the parasitic nematodes Wuchereria bancrofti, Brugia malayi and B. timori, afflicts more than 70 million people globally with a further 856 million people at risk [1]. In 2000, under the direction of the WHO, the Global Program to Eliminate LF (GPELF) was developed and was based on a comprehensive strategy to rid countries of LF by 2020 [2]. The Pacific Program to Eliminate LF (PacELF) commenced in 1999 to assist the countries and territories of the Pacific area, in recognition of the unique epidemiology and historically high number of cases within this region [3]
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