Prevention of tuberculosis transmission through medical surveillance systems

The increased flow of migrants from low-income to high-income countries in the past 5 years has raised the issues of migration-related social, economic, and health risks in many countries. Migrants are a vulnerable population who could be at risk of developing infectious and non-infectious diseases, or who could transmit pathogens to autochthonous populations.1Sandgren A Schepisi MS Sotgiu G et al.Tuberculosis transmission between foreign- and native-born populations in the EU/EEA: a systematic review.Eur Respir J. 2014; 43: 1159-1171Crossref PubMed Scopus (67) Google Scholar, 2Kunst H Burman M Arnesen TM et al.Tuberculosis and latent tuberculous infection screening of migrants in Europe: comparative analysis of policies, surveillance systems and results.Int J Tuberc Lung Dis. 2017; 21: 840-851Crossref PubMed Scopus (67) Google Scholar Thousands of people have migrated from low-income countries, where the tuberculosis incidence is high, to high-income countries, where the incidence is low. Although the mass transmission of mycobacterial strains from migrants has not been proven scientifically, owing to the limited relationships between migrant and autochthonous people, migrants are currently one of the most important population groups contributing to the national tuberculosis burden in western European and other developed countries.3European Centre for Disease Prevention and ControlWHO Regional Office for EuropeTuberculosis surveillance and monitoring in Europe 2017. European Centre for Disease Prevention and Control, Stockholm2017Google Scholar, 4Tsang CA Langer AJ Navin TR Armstrong LR Tuberculosis among foreign-born persons diagnosed ≥10 years after arrival in the United States, 2010–2015.MMWR Morb Mortal Wkly Rep. 2017; 66: 295-298Crossref PubMed Scopus (28) Google Scholar This epidemiological scenario implies social, health care, economic, financial, and public health consequences. The annual national tuberculosis incidence is proportionally attributable to migrants in half or more cases.3European Centre for Disease Prevention and ControlWHO Regional Office for EuropeTuberculosis surveillance and monitoring in Europe 2017. European Centre for Disease Prevention and Control, Stockholm2017Google Scholar, 4Tsang CA Langer AJ Navin TR Armstrong LR Tuberculosis among foreign-born persons diagnosed ≥10 years after arrival in the United States, 2010–2015.MMWR Morb Mortal Wkly Rep. 2017; 66: 295-298Crossref PubMed Scopus (28) Google Scholar This increasing burden of disease and the risk of transmission to susceptible population groups can hinder the path towards tuberculosis elimination targets. Most high-income countries have a tuberculosis incidence lower than 10 cases per 100 000 inhabitants; systematic implementation and scale-up of clinical (eg, appropriate diagnosis and treatment) and public health (eg, infection control measures) interventions can have a crucial role towards achievement of elimination. However, the increased pool of individuals with latent Mycobacterium tuberculosis infection represents a continuous source of new tuberculosis cases, reducing the pace towards a major reduction in tuberculosis incidence.2Kunst H Burman M Arnesen TM et al.Tuberculosis and latent tuberculous infection screening of migrants in Europe: comparative analysis of policies, surveillance systems and results.Int J Tuberc Lung Dis. 2017; 21: 840-851Crossref PubMed Scopus (67) Google Scholar, 5Sotgiu G Migliori GB Effectiveness of post-migration tuberculosis screening.Lancet Infect Dis. 2017; 17: 684-685Summary Full Text Full Text PDF PubMed Scopus (2) Google Scholar, 6Dara M Solovic I Sotgiu G et al.Tuberculosis care among refugees arriving in Europe: a ERS/WHO Europe Region survey of current practices.Eur Respir J. 2016; 48: 808-817Crossref PubMed Scopus (71) Google Scholar, 7Dara M Solovic I Goletti D et al.Preventing and controlling tuberculosis among refugees in Europe: more is needed.Eur Respir J. 2016; 48: 272-274Crossref PubMed Scopus (15) Google Scholar, 8Lönnroth K Migliori GB Abubakar I et al.Towards tuberculosis elimination: an action framework for low-incidence countries.Eur Respir J. 2015; 45: 928-952Crossref PubMed Scopus (542) Google Scholar, 9D'Ambrosio L Dara M Tadolini M et al.European national programme representativesTuberculosis elimination: theory and practice in Europe.Eur Respir J. 2014; 43: 1410-1420Crossref PubMed Scopus (132) Google Scholar, 10Sotgiu G Migliori GB Is tuberculosis elimination a reality?.Lancet Infect Dis. 2014; 14: 364-365Summary Full Text Full Text PDF PubMed Scopus (12) Google Scholar As underscored by the WHO guidelines on the management of latent tuberculosis infection,11Getahun H Matteelli A Abubakar I et al.Management of latent Mycobacterium tuberculosis infection: WHO guidelines for low tuberculosis burden countries.Eur Respir J. 2015; 46: 1563-1576Crossref PubMed Scopus (391) Google Scholar it is important to detect the population groups at highest risk of developing tuberculosis disease to decrease disease incidence and protect close contacts from infection. Implementation and appropriate functioning of national surveillance systems, integrated in the framework of national tuberculosis programmes, are core elements of effective tuberculosis control policies. In The Lancet Public Health, Leyla Asadi and colleagues12Asadi L Heffernan C Menzies D Long R Effectiveness of Canada's tuberculosis surveillance strategy in identifying immigrants at risk of developing and transmitting tuberculosis: a population-based retrospective cohort study.Lancet Public Health. 2017; 2: e450-e457Summary Full Text Full Text PDF Scopus (15) Google Scholar present useful scientific evidence proving the clinical and public health importance (and utility) of the national surveillance systems, particularly those focused on the migrant population. In a retrospective cohort study, the investigators describe the experience of the national tuberculosis medical surveillance programme in Alberta, Canada, in a sample of roughly 220 000 migrants recruited between 2002 and 2013. Foreign-born migrants represent the most important population group at risk of tuberculosis disease; the Canadian public health authorities have placed a special focus on this group to achieve the elimination targets. People who request to stay permanently in Canada undergo a pre-entry immigration medical examination. If diagnosis of culture-proven disease is made, the candidates should complete an entire course of anti-tuberculosis treatment in the country of residence. If positive inactive or old pulmonary tuberculosis is identified (at medical history or physical examination), individuals are referred (referrals) to the local public health services for an annual medical check (wait-and-see approach), which might include treatment of latent tuberculosis infection. Non-referrals are not included in the surveillance system. Asadi and colleagues found that referrals had a higher incidence of culture-positive pulmonary tuberculosis than did all non-referrals (incidence rate ratio 9·1, 95% CI 6·7–12·5), but a lower probability of transmitting M tuberculosis (71 total transmission events arose from the individuals with culture-positive pulmonary tuberculosis: three [4%] from referrals and 68 [96%] from non-referrals). The index referral cases did not cause secondary cases of disease, being less frequently sputum smear-positive. The investigators gave two possible reasons explaining the lower risk of M tuberculosis transmission: (1) the referrals' shorter stay in Canada, and (2) the lower rate of sputum smear-positivity following a rapid bacteriological or radiological diagnosis (the time lag from symptom onset to diagnosis is less than 2 weeks13Khan K Hirji MM Miniota J et al.Domestic impact of tuberculosis screening among new immigrants to Ontario, Canada.CMAJ. 2015; 187: E473-E481Crossref PubMed Scopus (22) Google Scholar) or a different phenotype. The present study has several merits: the findings can be inferred to countries with a tuberculosis epidemiology similar to Canada, being based on a solid methodology (study design and analysis), a large sample size, and a rigorous epidemiological system to capture information about M tuberculosis transmission (ie, conventional epidemiology based on contact tracing and molecular epidemiology based on DNA fingerprinting). The investigators have shown that the migrant population is a heterogeneous group, with some individuals at high risk of developing tuberculosis and deserving strict surveillance. A cost-effectiveness analysis of this public health approach is missing, but the findings are sufficiently strong to support the utility of this approach. The Canadian model is an example that could be implemented in other high-income countries. We declare no competing interests. Effectiveness of Canada's tuberculosis surveillance strategy in identifying immigrants at risk of developing and transmitting tuberculosis: a population-based retrospective cohort studyDespite a much higher incidence of pulmonary tuberculosis in referrals than non-referrals, referrals were 80% less likely to transmit tuberculosis. Rather than a focus on referrals, Canada could consider screening and treatment of latent tuberculosis in all migrants from high-risk countries—a group that accounted for 100% of secondary cases. 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