Domestic impact of tuberculosis screening among new immigrants to Ontario, Canada

Abstract

Background: All Canadian immigrants undergo screening for tuberculosis (TB) before immigration, and selected immigrants must undergo postimmigration surveillance for the disease. We sought to quantify the domestic health impact of screening for TB in all new immigrants and to identify mechanisms to enhance effectiveness and efficiency of this screening.

Methods: We linked preimmigration medical examination records from 944,375 immigrants who settled in Ontario between 2002 and 2011 to active TB reporting data in Ontario between 2002 and 2011. Using a retrospective cohort study design, we measured birth country-specific rates of active TB detected through preimmigration screening and postimmigration surveillance. We then quantified the proportion of active TB cases among residents of Ontario born abroad that were detected through postimmigration surveillance. Using Cox regression, we identified independent predictors of active TB postimmigration.

Results: Immigrants from 6 countries accounted for 87.3% of active TB cases detected through preimmigration screening, and 10 countries accounted for 80.4% of cases detected through postimmigration surveillance. Immigrants from countries with a TB (all-sites) incidence rate of less than 30 cases per 100 000 persons resulted in pre- and postimmigration detection of 2.4 and 0.9 cases per 100 000 immigrants, respectively. Postimmigration surveillance detected 2.6% of active TB cases in Ontario residents born abroad, and TB was detected a median of 18 days earlier in those undergoing surveillance than in those who were not referred to surveillance or who did not comply. Predictors of active TB postimmigration included radiographic markers of old TB, birth country, immigration category, location of application for residency, immune status and age.

Interpretation: Universal screening for TB in new immigrants has a modest impact on the domestic burden of active TB and is highly inefficient. Focusing preimmigration screening in countries with high incidence rates and revising criteria for postimmigration surveillance could increase the effectiveness and efficiency of screening.

Figure 1:

Onset of active tuberculosis (TB) relative to time of immigration among applicants for permanent residency (A) from within Canada and (B) overseas, 2002–2011. Bars with negative time values represent TB cases reported among people born abroad before they became permanent residents (55.6% of patients among in-Canada applicants). Among overseas applicants, bars with negative time values represent temporary residents, visitors and other people born abroad in whom active TB developed while in Ontario, who then left Canada, applied for permanent residency overseas and subsequently returned to become permanent residents in Ontario. Bars with positive time values represent TB cases among permanent residents stratified by whether they were referred for postimmigration surveillance.

Figure 2:

Proportion of people in Ontario with active tuberculosis (TB) that was potentially detectable through postimmigration surveillance, 2005–2011. *Includes all cases among residents born in Canada and those born abroad that were reported to the Ontario Ministry of Health and Long-Term Care from 2005–2011. People born abroad include permanent residents, temporary residents, visitors and undocumented immigrants. Percentages reflect the proportion of all active TB cases among people born abroad. Percentages may not sum to 100 owing to the rounding of values. †Patients in whom active TB developed before immigration include those who received their diagnosis in Ontario but were not permanent residents at the time (e.g., temporary visitors). These cases (n = 149) would not have been detectable through postimmigration surveillance. ‡Includes Ontario residents who received permanent residency status at least 3 years earlier (i.e., before 2002) and hence would not likely have undergone postimmigration surveillance as of 2005, temporary visitors who would not have had a preimmigration medical, and undocumented immigrants or other visitors to Canada who would not have had a preimmigration medical. These cases (n = 2481) would not have been detectable through postimmigration surveillance. §Time to development of active TB unknown for 3 patients. ¶Time to development of active TB unknown for 2 patients. **Includes cases of active TB that would have been potentially detectable through postimmigration surveillance of permanent residents. Of the cases that developed within 2 years of the patient’s immigration (n = 163), 155 may have been detectable on chest radiography (pulmonary, pleural or intrathoracic lymphadenitis) or peripheral lymph node examination, and 103 (2.6%) were actually detected through postimmigration surveillance.