Current gaps in survey design and analysis for molecular xenomonitoring of vector-borne neglected tropical diseases: a systematic review
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Objectives
Molecular Xenomonitoring (MX) is a surveillance method for vector-borne diseases where vectors are tested for molecular pathogen markers. Testing is typically on pools (groups) of vectors. MX is a sensitive and efficient complement to human based surveillance. However, there is limited guidance about the appropriate design and analysis of MX surveys. We reviewed the literature to understand the common objectives, survey designs, and analysis methods for MX surveys for two vector-borne neglected tropical diseases: lymphatic filariasis (LF) and onchocerciasis.
Methods
We searched peer-reviewed literature for studies published between 1999 and 2022 that presented the results of surveys that collected vectors in field surveys and used a molecular test for the presence of the causative pathogens for LF and onchocerciasis.
Results
A total of 76 studies (LF: 45; onchocerciasis: 31) across 30 countries were included in the review. The five most common objectives were determination of elimination status after mass drug administration, comparison of vector and human infection indicators, evaluation of an intervention, comparison of vector collection methods, and comparison of laboratory techniques. Nearly all studies used a cluster or hierarchical sampling frame to collect vectors (72/76), but very few studies accounted for this in their designs (2/76) or analysis (1/76). While few studies justified the number of vectors included in each pool (5/76), nearly all studies accounted for pooled testing when calculating pathogen prevalence from results (69/76). Few studies justified the number or selection of sampling sites or total sample size (16/76).
Conclusions
Published MX surveys for LF and onchocerciasis had varied objectives, study designs and analysis methods, but proper consideration of survey design was frequently missing from the analysis. There is a need for statistical tools and guidance to enable appropriate design and analysis of MX surveys while accounting for disease, objective, and context-specific considerations.
