HomeDespite the high prevalence of TB infection among foreign-born persons in Canada (see chapter overview), there are no routine post-arrival domestic TB infection testing and treatment programs. Risk factors associated with the highest rates of active TB among foreign-born populations include:15,23–40
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The global country or region of origin, especially sub-Saharan Africa, Asia and the Western Pacific regions (see Chapter 1: Epidemiology of Tuberculosis in Canada)
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Immigration category (refugees have roughly double the risk compared to other immigrants after arrival in host country)28
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Time since arrival in the host country (5 to 10 times higher in the first year and 2 times greater 1 to 4 years after arrival, as compared to 5 years or longer after arrival)30,32,34
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Underlying medical co-morbidities (see Chapter 4: Diagnosis of Tuberculosis Infection)
Most TB cases among foreign-born persons occur due to reactivation of previously acquired TB infection. However, based on evidence from studies of genetic clustering, 10-30% of cases may be due to infection acquired after arrival.41–45 The possibility of transmission within Canada should therefore be considered in the assessment of foreign-born TB patients, their family members (including those born in Canada) and other contacts, given the need for prompt diagnosis to limit the risk of onward transmission (see Chapter 11: Tuberculosis Contact Investigation and Outbreak Management).46 Current diagnostic tools for TB infection (IGRA and TST) do not sufficiently predict the likely occurrence or timing of reactivation.47 Only 5-10% of persons with TB infection will develop active TB, with 50% of this risk occurring (or having already occurred) within the first two years after infection.48 Shorter course rifamycin treatments are the preferred tuberculosis preventive treatment (TPT) regimens (see Chapter 6: Tuberculosis Preventive Treatment in Adults). Serious adverse events occur in <1% of those less than 65 years of age who take 4 months of rifampin; the rate increases in persons over 65 years of age and those with underlying medical co-morbidities.49–52
2.3.1. Targeted testing and treatment for TB infection among the foreign-born population in Canada
The probability that persons being considered for TB infection testing will have a positive test for TB infection and will develop active TB depends on the likelihood of TB exposure, the timing of exposure and the presence of risk factors for developing active TB. The decision to offer TB infection testing should consider the balance of benefits and risks to the patient. Only those who will benefit from treatment should be tested, so a decision to test presupposes a decision to treat if the test is positive. To make recommendations for TB infection testing among migrants, we chose a threshold of risk of developing active TB of 1% within 5 years among those with a positive test. We recognize that patients may have different values and preferences when considering the level of risk that may prompt a decision to initiate treatment. We estimated the risk of developing TB in different groups of immigrants based on age, TB incidence in the country of birth, time since arrival, immigration status (eg, refugees) and underlying medical co-morbidities, using a large cohort of immigrants who arrived in British Columbia between 1985 and 2012 who were followed for a median of 10 years.28,53 The immigrant groups that met the 1% threshold included those with underlying medical conditions with a high risk of TB reactivation and certain groups of refugees and recently arrived foreign-born persons with specified TB incidence in source country, age and time-since-arrival. Individualized TB infection testing may be considered for persons who do not belong to the groups listed below for whom this is recommended, after discussing the risk of reactivation and adverse events with the patient.
Recommendations
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We strongly recommend TB infection testing in all people (all ages) born outside of Canada with conditions associated with a very high risk* of TB reactivation (good evidence).
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We conditionally recommend TB infection testing in all foreign-born persons (all ages) originating from countries with a TB incidence ≥50/100,000† and with conditions associated with a high risk* of TB reactivation (poor evidence).
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We conditionally recommend TB infection testing in refugees originating from countries with TB incidence ≥50/100,000† who are aged ≤65 years as soon as possible after arrival and up to two years after arrival. Testing for those aged >65 years can be considered in the context of their individual reactivation risk profile and risk of adverse events (poor evidence).
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We conditionally recommend that TB infection testing may be considered for persons born outside Canada, originating from countries with a TB incidence >200/100,000,† who have low to moderate risk of TB reactivation and are aged ≤65 years as soon as possible and within five years of arrival. Screening for those aged >65 years can be considered in the context of their individual reactivation risk profile and risk of adverse events. At the individual provider-patient level, providers should discuss and emphasize the benefits vs risks of TB infection testing and treatment (poor evidence).
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We conditionally recommend against routine TB infection testing for people born outside Canada who have come from countries with a TB incidence of <50/100,000† and who have no risk factors for reactivation (poor evidence).
*See Table 2, Chapter 4: Diagnosis of Tuberculosis Infection.
†For TB incidence in individual countries see the World Health Organization TB country, regional and global profiles (https://worldhealthorg.shinyapps.io/tb_profiles/).54
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