In the attack phase, the method that was found to be effective in the pilot programme is extended to the whole area. Alternatively, the area can be covered in sequence, but if this is done, then measures may need to be instituted to prevent re-infection. Time tables and procedures are required to ensure that separate teams cover the area in a regular manner. Realistic targets are set and organization developed to make sure they are kept. The delay in one part will cause the delay of everything else.
During the attack phase, the number of cases found by the passive surveillance services will rapidly diminish, so progress is assessed by making serial surveys. Incidence is more useful than prevalence data; therefore, surveys are conducted at regular intervals in sample areas. However, this can pose a strain on relations with the population that is being sampled and areas of higher prevalence may be missed, so new sample areas may need to be used after a time.
To ensure that all the remaining cases are found, an active surveillance system can be established. This involves special workers, each with an assigned area which is visited on a regular basis. Active surveillance is no substitute for passive surveillance, the two should work closely together.
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