Abstract
BackgroundTB outbreaks in educational institutions can result in significant transmission and pose a considerable threat to TB control. Investigation using traditional microbiological and epidemiological tools can lead to imprecise screening strategies due to difficulties characterising complex transmission networks. Application of whole genome sequencing (WGS) and social network analysis can provide additional information that may facilitate rapid directed public health action. We report the utility of these methods in combination with traditional approaches for the first time to investigate a TB outbreak in an educational setting.MethodsLatent tuberculosis infection (LTBI) cases were screenees with a positive T-SPOT®.TB test. Active TB cases were defined through laboratory confirmation of M. tuberculosis on culture or through clinical or radiological findings consistent with infection. Epidemiological data were collected from institutional records and screenees. Samples were cultured and analysed using traditional M. tuberculosis typing and WGS. We undertook multivariable multinomial regression and social network analysis to identify exposures associated with case status and risk communities.ResultsWe identified 189 LTBI cases (13.7% positivity rate) and nine active TB cases from 1377 persons screened. The LTBI positivity rate was 39.1% (99/253) among persons who shared a course with an infectious case (odds ratio 7.3, 95% confidence interval [CI] 5.2 to 10.3). The community structure analysis divided the students into five communities based on connectivity, as opposed to the 11 shared courses. Social network analysis identified that the community including the suspected index case was at significantly elevated risk of active disease (odds ratio 7.5, 95% CI 1.3 to 44.0) and contained eight persons who were lost to follow-up. Five sputum samples underwent WGS, four had zero single nucleotide polymorphism (SNP) differences and one had a single SNP difference.ConclusionThis study demonstrates the public health impact an undiagnosed case of active TB disease can have in an educational setting within a low incidence area. Social network analysis and whole genome sequencing provided greater insight to evolution of the transmission network and identification of communities of risk. These tools provide further information over traditional epidemiological and microbiological approaches to direct public health action in this setting.
Highlights
TB outbreaks in educational institutions can result in significant transmission and pose a considerable threat to TB control
We report use of traditional epidemiological methods in combination with social network analysis (SNA) and whole genome sequencing (WGS) to investigate the transmission of TB within the educational institution attended by the suspected index case
Close contacts were screened in accordance with NICE guidelines [8]; we subsequently extended screening to students and staff who shared a course with either infectious case
Summary
TB outbreaks in educational institutions can result in significant transmission and pose a considerable threat to TB control. The public health response to these outbreaks varied in the extent of screening undertaken (students with/without educational institution staff and members of the public) and differing degrees of contact with the suspected index case (direct case contact or exposure to the same classroom). Current NICE guidelines state that a risk assessment should be carried out for sputum smear positive contacts of those who have shared a course whilst the case was potentially infectious. This should be extended to extracurricular activities based on infectious duration, infectivity, population susceptibility, and proximity of contact [8]
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