ESPEN 2021-2030 PC Forecasts: Brief technical summary

Methods and assumptions

Defining Implementation units (IUs)

Forecast calculations are developed at the IU level, using the most recent IU division reported by countries. These units are assumed to remain unchanged until 2030. National summaries are then calculated by aggregation.

Population estimates

IU-level population estimates were developed using official census data submitted through JAP reports. When this was not available, demographic data were compiled by a cohort of data consultants during country missions held in 2018 and 2019. Estimates of population growth rates have been obtained from the most recent World Population Prospects report (https://population.un.org/wpp/) and were used to generate demographic projections until 2030. This indicator is available at country level and then applied equally to the IU-level demographics.

Contemporary IU endemicity

Current endemicity for each PC NTD is defined as that reported through the most recent Joint Reporting Form (JRF) submitted by countries, accounting for results of recent surveys (impact assessments, mapping, re-evaluations) when they were reported to ESPEN. For those IUs with unknown endemicity (STH, SCH and LF mapping gaps, and IUs considered suitable for onchocerciasis elimination mapping) surveys are scheduled for 2020 or 2021. A conservative assumption is made that these surveys will indicate prevalence exceeding implementation thresholds, thus indicating the need for PC.

Annual PC projections

The number (and timing) of expected future rounds of PC are calculated for each IU based on contemporary endemicity, the number of effective rounds previously reported through to 2019, and the results of recent impact assessment surveys. When developing these projections, we are assuming that the forecasted MDA rounds will achieve effective coverage and that the impact assessment surveys are successfully passed namely, survey results prove the transmission has likely been interrupted.

Indicated PC strategy

For each IU, an indicated PC strategy is determined on an annual basis dependent upon (i) forecast NTD co-endemicity status, (ii) endemicity of loaisis, and (iii) suitability for triple therapy for LF.  The co-endemicity with other PC-NTDs is considered to establish the recommended MDA strategy and integrated surveys.

Disease-specific algorithms

Lymphatic filariasis

• Non-endemic implementation units (IUs) do not require treatment.
• Under post-MDA surveillance, IUs do not require treatment either.
• In countries also endemic for onchocerciasis (except Kenya, STP, Madagascar, Eritrea, Comoros, Zambia & Zimbabwe), endemic IUs require up to 5 effective (coverage >= 65%) consecutive MDA rounds using MDA1 (ALB+IVM) or MDA4 (ALBx2) schemes. Then, they are expected to conduct a pre-TAS survey. An additional MDA round before TAS1 has been included.
• In countries non-endemic for onchocerciasis, endemic IUs require up to 5 effective consecutive MDA2 (ALB+DEC) rounds (Coverage >= 65%) then go for pre-TAS.
  1. Those that have completed 4 MDA2 rounds require 1 effective round of MDA2, then go for pre-TAS.
  2. Those with 3 MDA2 rounds implemented require 1 effective round using the MDA5 scheme, then go for TAS.
  3. Those with less than 3 MDA2 rounds implemented require 2 effective rounds of MDA5, then go for TAS.

• Pre-TAS passed then TAS1, if not passed then 2 more MDA (Coverage >=65%).
• TAS1 passed then TAS2, if not passed then 2 more MDA (Coverage >=65%).
• TAS2 passed then TAS3, if not passed then 2 more MDA (Coverage >=65%).
• TAS3 passed then post-MDA surveillance, if not passed then 2 more MDA (Coverage >=65%).
• Post-MDA surveillance (passive or active regular monitoring of recrudescence or reintroduction).

Onchocerciasis

• Non-endemic implementation units (IUs) do not require treatment.
• Under post-MDA surveillance, IUs do not require treatment either.
• Endemicity unknown and not having yet received treatment with ivermectin, then considered mapping (Onchocerciasis Elimination Mapping, OEM).
• Endemic areas for onchocerciasis require up to 12-15 effective MDA rounds (coverage exceeding 80%) with ivermectin depending on the pre-control prevalence before implementing impact assessment.
• The current impact assessment strategy of choice for onchocerciasis is the STOP MDA survey: a first pre-STOP assessment is conducted in 3-5 first-line villages and if results in no cases then a more extended survey is followed (STOP MDA survey) targeting more villages: often 30 with a mix of the first-line villages and others across the IUs.
• If the stop MDA assessment indicates there is no longer transmission, treatment is interrupted, and an evaluation is conducted 3-5 yrs after the STOP MDA survey to confirm the interruption of onchocerciasis transmission. If the pre-STOP MDA or STOP surveys are not passed, then resume MDA.
• Endemicity unknown (or requiring remapping) but under treatment against LF can conduct concurrently OEM (first stage) at the time pre-TAS is scheduled, and then OEM (second stage) along with the TAS1, if the environmental conditions are suitable for the occurrence of onchocerciasis transmission. We are here using the modeled predicted environmental suitability to include an indicator of this suitability in the algorithm.
• The current WHO recommendations for programs require that they align the timing of lymphatic filariasis and onchocerciasis impact assessments. Where feasible, transmission assessment surveys (TAS) and epidemiological or entomological impact assessments can be conducted together to maximize resources and coordinate decisions on stopping treatment.

Soil-transmitted helminthiases (STH)

• Non-endemic implementation units (IU) do not require treatment.
• Low-prevalence IUs do not require treatment.
• Moderate-prevalence IUs require up to 5-6 consecutive effective (coverage exceeding 75%) PC rounds (once a year) and then impact assessment (TAS LF+STH/SCH if co-endemic).
• High-prevalence IUs require up to 5-6 consecutive effective PC rounds (twice a year) and then impact assessment (TAS LF+ STH/SCH if co-endemic).

Based on current WHO guidelines,

1. If the prevalence resulting from impact assessment (IA) is <2% then treatment is no longer required.
2. If the prevalence resulting from IA is >=2% and <10% then treatment is required once every 2 years for 3 rounds until the next IA.
3. If the prevalence resulting from IA is >=10% and <20% then treatment is required once a year for 5 rounds until the next IA.
4. If the prevalence resulting from IA is >=20% and <50% then treatment is maintained at the previous frequency for 5-6 years until the next IA.
5. If the prevalence resulting from IA is >=50% then treatment is required three times a year for 5-6 years until the next IA.

Schistosomiasis

• Non-endemic implementation units (IU) do not require treatment.
• Endemic areas showing prevalence below 10% IUs require PZQ to be available at the health facilities to treat cases individually if PC has not been initiated. If it has begun, continue at the established frequency until an impact assessment is conducted.
• Endemic areas showing prevalence >=10% require up to 5 consecutive PC rounds (once a year) and then an impact assessment should be conducted. All individuals older than 2 years are eligible for treatment.

Based on current WHO guidelines,

1. If no STH cases are detected in the impact assessment (IA) keep surveillance and test & treat in health facilities. After 5 years a new impact assessment should be conducted for verification.
2. If the prevalence resulting from IA is <10% (Low prevalence) then 1 MDA round every 2-3 years for 5 years. Then, repeat the impact assessment survey.
3. If the prevalence resulting from IA is >=10%-<50% (Moderate prevalence) or >=50% then 1 annual PC round for 5 years and then IA.
4. An additional round of PC should be delivered in hotspots within areas of high prevalence (>=50%).

Disclaimers

• The impact assessment surveys for STH and schistosomiasis lead to multiple prevalence scenarios, and the decisions to make regarding the treatment strategy (stopping or continuing PC, frequency, etc.) are conditioned by the resulting prevalence. 
• The estimates on treatment needs for women of reproductive age (WRA) have not yet been included in the forecasting algorithm since countries have not yet started to provide estimates of WRA. The new JAP report form released in July 2022 is collecting this demographic indicator.
• As new data is submitted by countries concerning treatment implementation and impact assessments, the projections will be updated accordingly.

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WHO advocate for integrated actions wherever possible. As such, estimates have been generated for all PC-NTDs that may coexist in the same geographical areas. Some PC-NTDs benefit from actions conducted by other programs. For instance, LF MDA interventions (using albendazole and ivermectin) target total population in areas where onchocerciasis and STH may also be present, regardless of their endemicity. These forecasts account for these potential synergies and co-endemicities when calculating treatment and survey needs.

For further information or to provide feedback on country-level and IU-level forecasts, please contact ESPEN through the ESPEN Data Portal feedback page.