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A good screening algorithm should have the following characteristics:

  • High specificity (to reduce the number of false positives, ideally around 70%)
  • High sensitivity (to reduce the number of false negatives, ideally around 90%)
  • Low Number Needed to Screen (NNS)
  • Low cost
  • Rapid and simple to apply
  • High client acceptability


The algorithm should be optimised so that the maximum number of cases can be detected with available resources.

Usually verbal screening using  symptom complex (4S) are used. However ACF campaigns targeting key and vulnerable populations (household contact persons, elderly homes etc.)can consider using X ray also as a screening tool. Chest X ray helps in picking up sub-clinical TB cases also which will be usually missed through verbal screening of symptoms.   

A more sensitive test like NAAT is preferred over sputum microscopy in ACF campaigns as the cases will be in early stage and may be missed by testing using Microscopy.





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Which of these is a condition for a good screening algorithm for ACF? Minimise false positive results Ensure that the maximum number of cases are diagnosed with available resources The algorithm may differ from place to place depending on the local TB burden among different subgroups All the Above 4 A good screening algorithm is one which ensures a high yield of cases, with minimum resources and ensures equitable access to TB care. This algorithm has to be optimised locally based on research and previous prevalence data among subgroups. 2008 Yes Yes

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