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The most desirable screening strategy is one with high total yield of true-positive TB cases, few false-positives, low NNS, low cost, a rapid and simple algorithm and high client acceptability. In practice, many of these factors can run in opposite directions, and multifactorial analysis is required. The ScreenTB online tool has been developed to assist in prioritizing risk groups for screening and choosing appropriate screening and diagnostic algorithms.
An algorithm for systematic TB screening should combine one or several screening tests and a separate diagnostic evaluation for TB disease, as recommended by WHO (12). A negative diagnostic test result may be followed up by further clinical evaluation if clinical suspicion of TB is still high. This could include re-testing with the same or another diagnostic method and/or close follow-up of clinical symptoms with or without chest imaging.
The tuberculin skin test, like the Mantoux test and interferon-g release assays should not be used in screening of TB disease (13, 34). These tests cannot distinguish TB infection from TB disease and cannot predict who will progress to TB disease. The role of these tests in decision-making for TPT is discussed elsewhere (4).
Individuals receiving TPT should be monitored at every contact with health-care providers. It is important to determine non-adherence as early as possible in order to take corrective action. Monitoring is particularly important at the beginning of treatment, when people are getting used to the routine and their medication. Afterwards, monitoring may be done monthly or more frequently as required for care of people on TPT or as per national policy.
A thimble connection (see Figure 3) is used with Class II type A2 BSC that is ducted to the outside. The thimble fits over the cabinet’s exhaust housing, sucking the air expelled from the cabinet into ducts that lead outside. A small opening (usually 5 cm wide) is maintained between the thimble and the cabinet’s exhaust housing. This opening enables room air to be drawn into the exhaust ducting system. The capacity of the exhaust system must be sufficient to capture both room air and the cabinet’s exhaust.
Class II BSCs differ from Class I cabinets in that they allow only air from a HEPA-filtered (sterile) supply to flow over the work surface.
A Class II type A2 BSC is shown in Figure 2. An internal fan draws room air (supply air) into the cabinet through the front opening and then into the front intake grill. After passing through the grill, the supply air is drawn upwards and through a HEPA filter before flowing downwards over the work surface.
