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Currently, about 22% of immigrants to Canada have a tuberculosis (TB), but very few were infected within the 2 preceding years, which is the period in which the risk for progression to TB disease is the highest, new research shows.
An analysis of country-specific data and Canadian census data showed that in 2021, the estimated prevalence of TB among immigrants to Canada was the lowest in Quebec (19%) and highest in Alberta and British Columbia (24%).
However, among all residents with TB who had migrated to Canada, only one in 488 had become infected within the high-risk period.
Study authors Jonathon R. Campbell, PhD, assistant professor of medicine, and Kevin Schwartzman, MD, MPH, professor of medicine, both at McGill University in Montreal, Canada, said that they were surprised by “the rarity of recent infection, even among people newly arrived in Canada.”
“Given the very low positive predictive value of current TB infection diagnostic tests for future disease, we need to know how common TB infection is to evaluate or predict the possible impact of any proposed screening and treatment programs,” they told Medscape Medical News.
The findings were published online on December 11, 2023, in the Canadian Medical Association Journal.
The investigators sought to support the design and implementation of TB prevention programs in Canada by estimating the prevalence and patterns of TB among residents who migrated to Canada from 168 countries.
They combined country-specific prevalence estimates with Canadian census data from 2001, 2006, 2011, 2016, and 2021 and found that the estimated overall prevalence did not change substantially over time. It was 25% in 2001, 24% in 2006, 23% in 2011, 22% in 2016, and 22% in 2021.
Between 2001 and 2021, the estimated prevalence decreased among immigrants from India, China, the Philippines, and the United States. The decrease was the greatest for immigrants from China (46% in 2001 to 28% in 2021).
Prevalence in 2021 and in earlier years increased with age at migration, ranging from 7% for people who became permanent residents when they were younger than 15 years to 62% for those who became permanent residents at an age ≥ 75 years.
The prevalence also increased with the incidence of TB in the country of origin. In 2021, the prevalence of TB varied from 8% among people from countries, with an incidence of less than 10 per 100,000 people to 35% among those from countries with an incidence of 200 per 100,000 people or higher.
Also, in 2021, 93% of all permanent residents and citizens born outside Canada lived in Ontario, Quebec, Alberta, or British Columbia. The estimated prevalence of TB was the lowest in Quebec (19%) and highest in Alberta and British Columbia (both 24%).
However, among all immigrant Canadian residents with TB in 2021, only 1 in 488 had become infected within the 2 preceding years, when the risk for progression to TB disease is highest.
“With current tools, screening for TB infection is most useful for persons who have recently arrived from countries where TB incidence remains high — particularly younger adults,” said Campbell and Schwartzman. “It is unlikely to benefit people who have lived in Canada for more than 1 or 2 years, unless they have other major risks for TB disease, such as recent contact with contagious TB or significant immune suppression.”
Commenting on the findings for Medscape, Ryan Cooper, MD, associate professor of medicine at the University of Alberta in Edmonton, said, “It’s a well-done study by a reputable team of researchers.” Cooper was not involved in the research.
The prevalences are estimates from mathematical modeling, he acknowledged, “but I think the results are consistent with what’s been observed on the ground. The study highlights that there’s a sizable reservoir of latent TB in Canada, particularly in our provinces that attract migrants. It also highlights the higher TB prevalence among Canadians who were born elsewhere, which is a health equity issue that warrants emphasis.”
The findings have implications for clinicians, Cooper added. Knowing, for example, that the TB prevalence among migrants from the Philippines and India is nearly 50% “should have a huge impact on your index of suspicion if you have someone from either of those countries with chronic symptoms.”
If clinicians are prescribing immunosuppressive or immune modulator therapies, he noted, “knowing how high the TB prevalence is in some specific populations should serve as a reminder to be sure to adequately screen those patients for TB infection and to provide preventive therapy.”
Understanding the TB burden is the first step for public health departments developing TB control programs, he added. “Further studies are needed to develop cost-effective strategies to tackle the problem and to better understand which individuals with latent TB infection will go on to develop active disease, so we can identify and screen those people,” Cooper concluded.
The study was supported by the Canadian Institutes of Health Research, and a coauthor was supported by a McGill University studentship award. Schwartzman reported support from the Bill and Melinda Gates Foundation and participation in a data safety monitoring board for Laurent Pharmaceuticals. He is a volunteer board member and executive committee member of the International Union Against TB and Lung Disease. Campbell and Cooper reported no competing interests.
Ante está noticia, nos inquieta como Clúster cuál puede ser la incidencia de esta enfermedad entre los migrantes que se quedan en nuestra ciudad.