Aims The tuberculin skin test (TST) and interferon-gamma release assay (IGRA) are screening tools for TB. The National Institute of Health and Care Excellence (NICE, 2016) guidance for paediatric TB recommend that TST is used for contact tracing, while IGRA is used for screening larger groups, for example in outbreaks. It also states that persons with TST readings of 5 mm or greater, regardless of BCG vaccination status, should be managed as though infected; compared with 15 mm or more (if BCG vaccinated), or 6 mm or more (if BCG unvaccinated) in the previous iteration of guidelines. We present the results of school screening following the diagnosis of smear positive pulmonary TB in an 11 year old. We aim to highlight the variable management outcomes under the different guidelines.
Methods Children were screened using TST following the diagnosis of smear positive pulmonary TB in an 11 year old. Children with negative or inconclusive results were rescreened. Any child with a positive TST had an IGRA test. Following the diagnosis of abdominal TB in a second child in the same class the screening cohort was expanded.
Results A total of 93 children were screened; 28 in the first round of screening and 65 in the second. All were BCG vaccinated. Twenty cases had positive (>5 mm) TST; 10 were >15 mm. 1 child had active TB, with identical genetic typing to the index case and 1 was referred to another facility. The remaining 18 cases were treated for latent TB infection; 17 had an IGRA3/17 (18%) were positive. Within the first cohort, 24 students with an initial negative TST were rescreened. 12/24 converted from negative TST to positive. Of these 12, only 2 (17%) had positive IGRAs.
Conclusion In this cohort, the IGRAs and TST tests were highly discordant. Had just IGRAs been used, 14/17 (82%) children with positive TST would not have received LTBI treatment. Persistently negative IGRAs on completion of treatment in 10 children with TST conversion were especially concerning as potential false negative tests. Clinicians should be aware of potentially missing cases of TB infection if IGRAs alone are used for screening.
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