SCH Oversampling Technical Advisory Group Meeting

Discussion Summary

The TAG appreciated hearing about the field work in Ghana and seeing the preliminary results. Participants were impressed by the level of effort undertaken by the team in Ghana to generate such a wealth of information in such a relatively short period of time. There was a lot of discussion regarding the heterogeneity of S. haematobium prevalence seen across the three districts, which ranged from some villages along Lake Volta with greater than 50% prevalence to more inland villages with 0% prevalence. One member suggested that there could be more than one snail species in the region that may be driving some of the differences seen. The TAG also expressed interest in using the data to investigate if positive children in low prevalence areas getting exposed locally or if their infection due to exposure occurring in other parts of the region.

The group discussed the challenges with small sample size and the need for mop-up activities in Ghana. For the future study sites, the TAG recommended that communities not be excluded from the sampling frame due to few inhabitants for fear that this might induce bias. Instead, the TAG recommends that field teams immediately conduct additional sampling in a neighboring community when the observed sample size in the selected community is small. It was noted that clear guidance on how to pick these neighboring communities will be necessary. Ideally, a neighboring community should have a shared water source, shared school or be with 3km of the original community. A request was made to add a question on whether children have received MDA never, once or more than once in future sites.

On the topic of data collection and analysis, a clarification was made that ESPEN’s requirement for AFRO ERC approval is not new, but rather an existing requirement that is newly enforced. The TAG was appreciative of the effort to collect and store additional specimens for future SCH diagnostic testing. It was noted that FIND is organizing a biobank for NTDs and is supporting a new CAA RDT that uses whole blood. While this new CAA RDT will not be ready for testing in the SOS field sites, if greater than 50ul of whole blood is preserved in EDTA tubes, it could be possible to run the test from the preserved specimens. The SOS organizing team will explore whether any country would be able to collect and store whole blood specimens (the present plan was to only store dried blood spots).

When it comes to the analysis plans the TAG was onboard with the analyses outlined by the presenters. It was noted that if future sites lack geo-referenced information for all villages, it would be possible to use assign population to locations using population density maps. One can assign local population proportional to local density by using the sampled locations to determine the relevant multiplier. With regards to the survey designs under consideration, a concern was raised to ensure that the designs are flexible to local conditions. For example, rather than require 30 individuals per site, consider, “sample 30 children per site, but if 30 children do not exist, sample all the children.” A TAG member reminded the team to take into account the new WHO SCH guidelines, which call for a 10% treatment threshold, when designing classification (LQAS) surveys.