Tuberculosis in Canada: Global view and new challenges

Despite intensified global efforts, the number of cases of tuberculosis (TB) worldwide is increasing. The World Health Organization estimates that more than one-third of the world's population (two billion people) is infected with Mycobacterium tuberculosis. There are 8.4 million new cases annually, accounting for nearly two million deaths, making it the second leading cause of death from a single infectious agent (1). In Canada after decades of declining rates, the reported incidence of TB has reached a plateau since 1987. In 2000, 1694 cases (5.4 per 100,000) of new active and relapse TB were reported to the Canadian Tuberculosis Reporting System (2). Ten per cent to 15% were paediatric cases. Children are not only at higher risk for progression from infection to disease, but they also are at increased risk of complicated TB (miliary, meningitis). Furthermore, TB infection in children poses a long term public health threat by increasing the pool of infected people from which future cases will arise if they are not appropriately treated. The emergence of drug-resistant TB strains, the interaction with human immunodeficiency virus/autoimmune deficiency syndrome (HIV/AIDS) and the increase in population movements around the world have greatly increased the potential for resurgence of this disease in Canada. Foreign-born people, which comprise 18% of the Canadian population, accounted for 65% of all reported cases in 2000. More than 90% of all TB cases in the world occur in developing countries, and the majority of immigrants and refugees come from countries with incidence of TB up to 20 times higher than that in Canada. The distribution of TB cases among foreign-born people reflects changing immigration patterns. Furthermore, the incidence of disease is highest in the first few years after arrival, with 10% of TB cases developing within the first year of arrival, 17% within two years and 35% within five years. Recent immigrants, as opposed to Canadian-born individuals, tend to be of working age and parents of young children when they develop the disease. TB within this group may therefore have a major socioeconomic and epidemiological impact, particularly on the young population. Moreover, isolates from foreign-born cases were four times more likely to be drug-resistant and six times more likely to be multidrug-resistant (MDR) than those of Canadian-born individuals. The risk factors for acquired drug resistance such as previous TB treatment, noncompliance with medication (nonsupervised treatment) and the incorrect prescription of an anti-TB regimen by medical staff are well-known. In developing countries, primary and acquired resistance are becoming increasingly prevalent. With increasing migration, it is expected that these strains will pose a serious threat as they spread rapidly around the world (3). In Canada, drug resistance has not yet reached high prevalence: in 2001, 10.1% of isolates demonstrated some type of drug resistance and 1% showed MDR TB (4). Children in contact with contagious drug-resistant adults may be infected and constitute a pool from which cases of drug-resistant TB will arise in the future (5). TB infection is most commonly found among four groups in Canada: those born from TB-endemic countries, Aboriginal people, inner city poor and homeless individuals, and elderly people (6). Co-infection with HIV is not uncommon among inner city people with history of injection drug use, and recent data suggest that the incidence of HIV/AIDS is increasing among Aboriginal natives (7) and those born in TB-endemic countries (8). HIV infection, in particular, poses a high risk of reactivation of latent TB, potential rapid progression of recently acquired infections and possibly a more contagious disease. Those characteristics, combined with the global HIV pandemic, are amplifying the worldwide incidence of TB (9). The recent epidemiological trend noted above indicates that TB control is now entering a new phase in Canada. Transition from low incidence to elimination will be achieved through a national commitment to TB elimination, with focus on high risk groups (eg, Aboriginal people, foreign-born individuals) and further involvement in the international fight against TB (10). Providing public health services to TB patients presents substantial challenges. These challenges not only apply to foreign-born individuals but also Aboriginal people in other regions of Canada, particularly in the presence of complicating risk factors such as drug-resistant disease. Cultural and linguistic barriers as well as economic limitations interfere with obtaining medical care, good adherence to prescribed therapy and participation in contact investigation. Culturally sensitive health care services consisting of providers for Directly Observed Therapy, language interpreters, incentives, enablers, translated educational material and convenient referral mechanisms are key elements for success in the control of TB among recent immigrants. Rapid diagnosis of active disease is essential to prevent the transmission of TB to contacts. Because children almost always acquire TB from an infectious adult, the most efficient method of finding infected children is through contact investigation of adults with contagious pulmonary TB. If a child is the initial identified case, tracing and testing of adult contacts must be done to find the adult source of the child's infection (11). Directly Observed Therapy should be the standard of care for all patients: a health care worker or designate must be present to observe the patient while he is taking all the prescribed doses. This universally recommended practice (12) has been a very effective tool in the control of drug resistance (13). HIV testing, along with pretest and post-test counselling, must be routinely offered to all cases of active TB. Targeted tuberculin testing and treatment of persons with latent TB infection is a strategic component of TB control. The goal of testing is to identify people who, because they are at increased risk for the development of active TB, would benefit from treatment of the infection. The patients who will benefit from testing are those who either are at an increased risk of TB infection (close contact of active contagious TB, recently immigrated people from countries with high prevalence of TB), or have a condition that increases their risk of progression to active TB (HIV-infected people, underlying chronic medical condition) (14). Targeted school-based screening programs for recently immigrated children, although controversial, appear to be a promising option (15), especially when the prevalence of TB infection is 20% or more in the targeted group and if adherence to preventive therapy is greater than 60% (16). Such innovative, targeted activities that require partnerships among schools, local health care providers and public health departments must be further evaluated for their ability to meet the objectives for finding latent TB infection and ensuring that children are appropriately treated. Education and training about TB are essential for sustainable control programs. Training should be directed not only to health care professionals (so they will ‘think TB’ in the first place), but also to the patients, community members and political leaders to increase their awareness and understanding about the control and the prevention of TB infection and disease. Finally, basic, epidemiological, public health and community-based research play a key role in a national strategy to eliminate TB in Canada, and must be promoted and supported accordingly by all potential funding sources. The changing epidemiology of TB in Canada and in other countries, including the emergence of MDR TB and the spreading TB-HIV co-epidemic, poses new challenges to control and eliminate ultimately the threats caused by TB in this country. Canada should acknowledge the need to address the global TB epidemic to have an impact on the significant proportion of Canadian cases that occur in foreign-born people. Accordingly, Canada should invest resources and expertise to provide assistance to TB control programs in countries where the disease has high prevalence. It is time to act.

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.