We describe an integrated NTD mapping methodology (Integrated Threshold Mapping) that can be used as an operational tool by Ministries of Health in NTD-endemic countries to determine if the threshold needed to launch disease-specific public health intervenions has been reached. With the recent increased interest in NTDs, there is a real need for an integrated mapping approach that can provide district level data in a timely manner 
. In developing this ITM methodology, we sought to balance epidemiologic rigour with field practicality, resulting in an approach that can be used only for determining where public health interventions are needed. With the exception of some minor modifications for trachoma, we have retained the key indicators and age groups used in the disease-specific WHO mapping guidelines, but have adapted the sampling methodologies. This ITM methodology reduces costs, and the need for manpower and resources, and gives MoHs a simpler and quicker way to estimate their NTD needs.
The first step in making a NTD action plan is to evaluate the existing data, including the methodology and time of the data collection, and to determine whether any factors that could influence the prevalence of the disease have changed since the data were collected. The second step is to collect data where existing data are missing or out of date; our ITM mapping protocol was designed for this purpose. Because it will be rare that all four NTDs will need mapping in any one district, the methodology consists of disease-specific modules. For each specific situation, modules can be combined to create the situation-specific NTD integrated protocol .
To understand the value and limitations of this protocol, it is critical to understand that this protocol is not claiming to provide epidemiologically correct prevalence data because both the villages and the individuals tested were not randomly selected. First, this implies that we cannot recommend using findings from this methodology as a baseline for measuring impact at the district level. This is also not possible for the WHO recommended mapping protocols for schistosomiasis, STH and LF, but it is the case for the trachoma WHO methodology. A possible second implication could be that the WHO recommended threshold could not be used when using this methodology; but here again, this would only be an issue for trachoma, bearing that the WHO methodology does not provide epdemiological correct prevalence figures for schistosomiasis, STH and LF.
One barrier to integrated mapping of NTDs is the misconception that mapping can only be integrated if all testing is done using the same age groups. In our ITM mapping protocol, we insisted on using the program-specific age groups as indicated by WHO with the exception of some adaptation for trachoma. The advantage of using these established age groups was that the WHO thresholds were applicable and that few people had to undergo multiple tests and examinations; only in a limited number of cases were people asked to undergo more than one test or examination. In each village, we chose to use a convenience sample for reasons of field practicality. Asking people of different ages to come to a central location in each village facilitated data collection and was much more time-efficient than house-to-house visits, such as those used in the WHO trachoma protocol. As the field testing in both countries showed, the data of both methodologies resulted in the same public health recommendations.
The ITM protocol maintains the WHO-recommended disease indicators and thresholds for LF, schistosomiasis and STH, but we used a novel sampling frame for more practical field implementation. To improve the representativeness for the TF indicator, we selected a pre-determined number of children between the ages of 1–5 and 6–9. This was intended to prevent biased estimates in case the 6–9 year age group made up the majority of children being graded for trachoma because prevalence rates are highest in 1–5 year olds. Although current WHO guidelines measure trichiasis in adults of both sexes as a standard indicator, literature shows that different adult age groups have been used to determine TT prevalence 
. After consultation with trachoma experts, we decided to use women above the age of 15 yrs 
Because the ITM methodology is focused on public health action, the sampling frame is directly linked to the implementation unit for MDA for each of the NTDs. Based on field experience, we decided to slightly modify those MDA implementation units to make public health interventions more feasible in the field, as shown in . Because a village-centered approach is difficult for implementation and supervision for a large-scale national program, we decided to use the district as the primary implementation unit for STH as it is recommended by WHO for LF and trachoma. Our methodology found the same public health intervention for trachoma and for STH. For STH, both methodologies concluded that no intervention was necessary, which confirmed the reliability of our methodology in the two countries. The LF testing was included to validate only the field feasibility of integrateing testing for four NTDs. In the case of schistosomiasis, a disease that is very focal in nature, and for which treatment medication is costly and in limited supply, we feel that it would be more appropriate to use the sub-district as implementation units to determine needs for treatment because a district-based approach may result in overtreating or undertreating subpopulations within the district 
. Our results show that by using the sub-district as I.U., the MDA will be more targeted to people at risk. In our study, when the WHO-recommended ecological zone was used as the implementation unit, highly endemic (prevalence of >50%) or low endemic (prevalence of <10%) sub-areas of the district were not identified, but were identified by the integrated methodology. As a result, using the WHO protocol would have meant that tens of thousands of people living in highly endemic areas would not have received treatment, and that other people not in need of treatment would have been treated, as would have been the case in Senegal.
The integrated approach proved to be more efficient in cost, transport, time in the field and the use of human resources. Because transportation and per diems are variables that significantly increase the cost of mapping, we created one small team of experienced technicians already active in the national MoH program instead of using multiple disease-specific teams. We decided to limit the number of team members to five by capitalizing on their laboratory expertise in parasitic diagnostic techniques mastered during their lab technician training. Each member of the team performed multiple tasks, which increased time and energy efficiencies and also made planning and field organization easier. We also counted on the strong engagement of local staff as we saw this as capacity building of district, dispensary, and village health staff. Although the team members from the different NTD programs were initially reluctant to work as one team, because it was a new concept, this hesitancy evaporated over the course of the survey. The team members also noticed that resources were used more efficiently compared to the WHO methodologies: the ITM methodology used one vehicle to transport the team, versus 3 used in the WHO methodologies, employed a 5-member team instead of a 7-member team, and took about half as much time to implement as the WHO methodologies.
It is also important to mention that certain cost savings from integrated mapping such as time saved by only having to plan one survey compared with several different protocol meetings and logistic preparations is priceless for overburdened health staff. In addition, the workload for all the preparations and supervision can be shared among different program coordinators.
It is worth mentioning that cost savings are just a single variable that justifies conducting integrated surveys: mapping is often the first field activity of an integrated NTD program, and the creation of the team demonstrated the concept of integrating vertical programs to all levels of the MoH and this first activity can help with further collaboration for implementing integrated public health interventions.
Although the ITM methodology resulted in substantial cost savings compared to the WHO methodology, the cost depends on the number of sub-units in a district. This means, for example, that the sampling size for schistosomiasis could be much higher using the ITM methodology than using the WHO methodology. However, this would result in a more targeted MDA for schistosomiasis, which is important because there is limited availability of donated praziquantel.
The results from both the ITM and WHO methologies indicate that health workers are not always well-informed about where schistosomiasis is most prevalent. The results show that treatment decisions, based on the purposely-selected villages, did not systematically result in more treatments than those based on the randomly-selected villages.
We encountered some limitations in conducting the integrated mapping. We are comparing a convenience sampling for schistosomiasis and STH mapping with an accepted WHO convenience sampling. Ideally, we would have compared both methods to an independent, “gold standard” survey methodology. The main limitation for the trachoma mapping is that a total of nine of the 60 trachoma villages sampled were selected for both methodologies. To decrease the burden of the inhabitants by not having the same children examined twice, we included the data collected in the integrated mapping for the WHO method and added only 30 children by visiting the households. For three villages, the selection bias was limited because the villages were so small that the likelihood that all the children in the integrated method would have also been included by visiting the houses was very high, but for the other six villages, a selection bias was likely introduced because up to 62% of the sample was selected by convenience only and those persons would maybe not have been included if the sample was collected randomly.
This study shows a novel integrated mapping protocol to determine whether thresholds for public health interventions have been reached. The approach is logistically practical, cost-efficient and flexible. For schistosomiasis, our approach also results in more targeted MDAs compared with the district level implementation currently adapted by most integrated NTD program. The protocol uses mainly the age-specific disease indicators as recommended by WHO. Further, it sets the stage for all of the following integrated program activities essential for NTD elimination and control. Based on the lessons learned from the implementation in the first two countries and feedback we received form NTD colleagues, we do recognize that this novel mapping approach requires some modification to ensure that the most useful data are collected. For this reason, we are currently field testing an adapted protocol with all villages selected randomly among other minor changes.