TST has the advantage of being inexpensive and not requiring a laboratory infrastructure. However, due to overlap with non-M. tuberculosis antigens (including those found in the BCG), specificity is lower than for IGRA, especially in younger children. It is also a test that requires two patient visits. Newer TB-specific skin tests have been developed and are now recommended by the WHO [28]. IGRA testing is more expensive and requires a laboratory, but only requires one patient visit and has improved specificity compared with a conventional TST. In reality, none of these tests is widely available in low-resource settings, and the WHO has provided decision algorithms that do not rely on TBI tests to guide treatment decisions for children being considered for TPT (figure 1). Decision making in children and adolescents with presumptive TB To diagnose a child or adolescent with TB disease, the first step is to decide if they may have presumptive TB. This screening process (whether active or passive) serves to exclude children and adolescents at low risk of TB, thereby focusing diagnostic tools on those with a higher risk of disease. The WHO defines someone as having presumptive TB if they have unremitting symptoms lasting 2 weeks (any one of cough, fever, not eating well or anorexia, weight loss or failure to thrive, fatigue, reduced playfulness or decreased activity). Confirmed and clinically diagnosed TB disease Once a child or adolescent has been identified as having presumptive TB, a decision must then be made as to whether to start TB disease treatment or not. To inform this decision, the traditional approach is to take a full history, carry out a clinical examination, conduct host immune tests if relevant, obtain samples for microbiological analysis and complete imaging (table 1). TB disease is confirmed if a microbiological test is positive for M. tuberculosis, but due to the paucibacillary nature of child TB, most younger children will not have confirmed disease. As children get older and enter adolescence, the proportion with confirmed disease increases. The confirmation rate increases incrementally if more samples are sent for microbiological testing. Those who are identified with TB disease without microbiological confirmation are described as having clinically diagnosed TB disease. The health worker may prescribe antibiotics to the child if they are concerned about TB but do not believe they have sufficient evidence for TB treatment. Symptoms, signs and radiology often resolve due to time or antibiotic treatment for non-TB causes. If the features persist after a couple of weeks and after the antibiotics, the probability of BOX 1 WHO recommendations for active screening and TPT Children and adolescents living with HIV as part of the comprehensive HIV care package#: 12 months with history of contact with a person with TB and in whom TB disease has been excluded 12 months and living in a high-TB-burden setting, in whom TB disease has been excluded, and regardless of history of TB contact All children who have completed TB treatment Children and adolescents, irrespective of HIV status, who are household contacts of a bacteriologically confirmed PTB case, in whom TB disease has been excluded Children who are candidates for anti-TNF treatment, dialysis, or organ or haematological transplant, or who have silicosis Children and adolescents who are immigrants from high-TB-burden countries, are homeless, or who use drugs or are in prison #:all children and adolescents living with HIV regardless of ART status should be screened for TB at every attendance using the following symptom screen: (any) cough, fever, poor weight gain or close contact with a person with TB. If they have any one of these symptoms, they should be investigated for TB. Data from [25]. https://doi.org/10.1183/2312508X.10025322 213 CHILDREN AND ADOLESCENTS |E. LÓPEZ-VARELA ET AL.