Transmission Assessment Survey (TAS)

To undertake a Transmission Assessment Survey (TAS), a Pre-TAS must be undertaken to meet the criteria for eligibility.  To do this Evaluation Units (EU) need to be defined either by combining or dividing or leaving as defined the Implementation Units (IUs).  If IUs are combined the resulting EU should have the following characteristics: (i) IUs in an EU are usually contiguous; (ii) All IUs should have had at least 5 effective (>65%) rounds of MDA and in all sentinel and sport check sites the prevalence of Mf is <1% or the Ag is <2% at all sites after the last effective round; (iii) All areas in an EU should have similar epidemiological features and LF transmission dynamics and (iv) the population should not exceed 2 million.

TAS 1, 2 & 3
TAS is a standardized method based on blood tests that is used to decide whether to stop MDA.   ‘Passing’ a TAS means that the prevalence of LF in the Evaluation Unit has been lowered to a level at which transmission is probably no longer sustainable and recrudescence is unlikely to occur even in the absence of MDA.

The target population of a TAS is children aged 6-7 years.   The rationale is that children in this age-group should have lived most (or all) of their lives during MDA in the area being surveyed.   If adequate drug coverage was achieved, the infection rate in the population should have decreased with little potential transmission, so that young children are probably protected from infection.  Therefore, any positive results in young children in areas in which MDA was successful are likely to indicate recent transmission.

Click here for the WHO position statement "Transmission assessment surveys in the global programme to eliminate lymphatic filariasis 

Click here for the WHO manual for national elimination programmes: Lymphatic filariasis: monitoring and epidemiological assessment of mass drug administration