Canada's blanket practice of screening all newly arriving immigrants for tuberculosis (TB) is highly inefficient and should focus on only those arriving from countries with high rates of TB, according to research published in CMAJ (Canadian Medical Association Journal)
"Programs screening for active TB in immigrants from low-incidence countries incurs substantial costs to the federal government, the provincial and territorial ministries of health, local health authorities, medical providers and the immigrants themselves without showing evidence of substantial public health benefit," writes Dr. Kamran Khan, scientist in the Li Ka Shing Knowledge Institute of St. Michael's Hospital and associate professor in the University of Toronto's Division of Infectious Diseases, with coauthors.
All immigrants to Canada are screened for contagious forms of TB by chest x-ray before emigrating, and some receive secondary surveillance after settling in the country. In Canada and the United States, two-thirds of TB cases are in residents born abroad, although they make up a smaller proportion of the population (one-fifth in Canada and one-eighth in the US).
In a study of 944 375 immigrants who settled in Ontario, Canada's largest province, between 2002 and 2011, researchers found that a large portion (87.3%) of TB cases detected before immigration came from people born in just 6 countries: Afghanistan, China, India, Pakistan, the Philippines and Vietnam.
"New immigrants arrived in Ontario from 214 countries during the study period, but all cases of active TB detected through preimmigration screening or postimmigration surveillance occurred in patients who originated from just 35 countries," write the authors. "Our findings highlight the inefficiency of universal screening for TB among new immigrants independent of the incidence of disease in their countries of origin."
They suggest that immigrants from areas with low rates of TB, such as Australia, New Zealand, the US and Western European countries, should not be routinely screened for TB.
The study also indicates that the current practice of surveillance after arrival is marginally effective, and unnecessary for some immigrant populations.
Countries such as Canada that receive large numbers of immigrants from areas with a high incidence of TB should also consider increased investment in international TB prevention and management.