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Class I BSCs work by drawing unfiltered room air in through a front opening, passing it over the work surface, and then expelling it through an exhaust duct.
Class I BSCs protect workers but do not protect work products (such as specimens or cultures) against contamination because unsterilized room air is drawn over the work surface.
To address specific potential risks, the following biosafety requirements¹⁴ ¹⁵ should be established in a low-risk TB laboratory.
1. Use of bench spaces: The bench used to process specimens for direct sputum-smear microscopy or the Xpert MTB/RIF assay should be separate from areas used to receive specimens and from administrative areas used for paperwork and telephones.
Overall, serious adverse events leading to death or requiring withdrawal of TPT occur rarely. It is nevertheless critical to identify any sign of drug toxicity as soon as possible and to manage it immediately, particularly because people on TPT are usually healthy. Unmanaged drug toxicity may not only harm individuals but can also damage the reputation of a programme and result in widescale suspension of TPT due to loss of public confidence. As in any preventive action, health-care providers must weigh the risks and benefits of TPT for each individual.
The tables below contain modelled estimates of the performance and outcomes of the 10 screening algorithms described above, when applied to a population of 100,000 people being screened, across three different TB prevalence settings: 0.5%, 1% and 2%.
1 – Screening with cough
2 – Parallel screening with cough and CXR
3 – Sequential positive serial screening with cough and CXR
4 – Sequential negative serial screening with cough and CXR
5 – Screening with any TB symptom
Since 2011, WHO has recommended that people living with HIV be systematically screened for TB disease at each visit to a health facility. The recommendation is based on the high risk of this group for TB and mortality and a lingering gap in case detection in this population. In 2019, people with HIV were at 18 times greater risk for incident TB than people without HIV and close to one third of deaths from AIDS were due to TB (2). Only 56% of the total estimated number of HIV-positive incident TB cases were detected in 2019 (2).
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.