Transmission assessment surveys

Transmission Assessment Survey (TAS): A survey designed to measure whether evaluation units have lowered the prevalence of infection to a level where recrudescence is unlikely to occur, even in the absence of MDA interventions.

Evaluation is necessary to determine whether the programme has achieved its objective of reducing levels of microfi lariae in endemic populations to an extent where transmission is likely no longer sustainable. Programmes must be able to assess whether MDA has succeeded in lowering the prevalence of infection to a level where recrudescence is unlikely to occur.

Transmission Assessment Surveys (TAS) are designed to help programme managers determine whether areas have reached this critical threshold of infection can be used to automate the calculations for determining the appropriate survey strategy. Th e design of the TAS is fl exible in
order to best fit the local situation; it depends upon factors such as the net primary school enrolment ratio, the population size, the number of schools or enumeration areas and the feasibility of different survey methods.

While the TAS provides helpful evidence to national programmes regarding the decision to stop MDA, programme managers must thoughtfully consider the decision about whether to stop or to continue MDA.