Training in monitoring and epidemiological assessment of mass drug administration for eliminating lymphatic filariasis Module 2 Eligibility for a TAS
Learning objectives By the end of this module, you should understand that the eligibility of an IUfor a TAS is assessed on the basis of: • epidemiological drug coverage (programme coverage) • prevalence of infection at sentinel sites • prevalence of infection at spot-check sites
Overview • Eligibility criteria for a TAS • Epidemiological drug coverage (programme coverage) • Sentinel and spot-check surveys • Confirming eligibility
Eligibility criteria for a TAS In order for a national programme to start planning a TAS, the following criteria must be met in each IU: • At least five rounds of MDA were completed. • ≥ 65% epidemiological drug coverage achieved at each round. • Sentinel site: prevalence of Mf < 1% or prevalence of Ag < 2% after last effective round at all sites • Spot-check site:prevalence of Mf < 1% or prevalence of Ag < 2% after last effective round at all sites
Epidemiological drug coverage • Epidemiological drug coverage (programme coverage) is defined as "the proportion of individuals in an IU who actually ingested the medicines" No. people reported to have ingested the medicines = X 100 Total population in IU • To reduce the prevalence of Mf in infected individuals to the threshold below which transmission is assumed to be no longer sustainable, at least 65% of the total population in each IU must ingest the medicines in at least five rounds of MDA.
Sentinel and spot-check surveys • Blood surveys at sentinel sites are used to establish the baseline infection level and to monitor the impact of MDA on infection prevalence periodically. • Once a sentinel site is selected, it should continue to serve as the sentinel site throughout the programme. • Blood surveys at spot-check sites are used to confirm that the results of sentinel surveys represent the infection level in the entire IU. • At least one spot-check site is selected for each sentinel site.
How many sentinel and spot-check sites are needed in each implementation unit? • At least one sentinel site per 1 million people • At least one sentinel site in each IU; more sites may be selected when resources allow • Smaller IUs may be served by one sentinel site. • Combined IUs should be contiguous and have similar epidemiological characteristics. • Combined IUs should have conducted MDA at the same time. • The advice of WHO and the RPRG may be required.
Characteristics of sentinel and spot-check sites • The population should be at least 500 people (to collect samples from at least 300 people aged > 5 years) • Should be in an area of high transmission: high disease or parasite prevalence or vector abundance • or an area where difficulty in achieving high drug coverage is anticipated • No prior MDA for onchocerciasis • A stable population
When should surveys be conducted? • Baseline assessment: before first MDA • Mid-term evaluation: at least 6 months after third MDA (optional) • Follow-up survey: at least 6 months after fifth effective MDA Round of MDA 1 2 3 4 5 Mapping TAS Mf and/or Ag prevalence (follow-up) Mf and/or Ag prevalence (optional) Mf and/or Ag prevalence (baseline)
When should surveys be conducted? • Target population • Convenience sample of at least 300 people • All members of the population in all age groups > 5 years (including pregnant women) • When the population is too large, a part can be chosen. • Diagnostic test • Blood film for prevalence of Mf • Immunochromatographic test (ICT) for Ag rate if resources allow (in W. bancroftiareas)
Confirming eligibility to conduct a TAS • Before assessing the eligibility of an IU, programme managers should compile all necessary records and complete the ‘INTRO’ and ‘ELIGIBILITY’ worksheets of the TAS Eligibility and Reporting Form. • The form helps in deciding whether the time is appropriate to conduct a TAS. • The form should be reviewed by the RPRG before the survey is planned.