March 30, 1999
To:Board of Health
From:Dr. Sheela V. Basrur, Medical Officer of Health
Subject:Update on Tuberculosis
To provide information to the Board of Health about the epidemiology of Tuberculosis (TB) in the City.
Source of Funds:
It is recommended that this report be received for information.
In January 1999, I identified TB control as a priority in the harmonization of Public Health programs and services across
the new City. TB resurgence is an ever present risk, given the continued migration of peoples from TB endemic countries
into Toronto, the high prevalence of HIV infection and the presence of social conditions which facilitate the spread of TB
in Toronto. On February 22nd, 1999, the Board of Health adopted recommendations to harmonize the TB program at the
optimal service level.
This report provides an analysis of TB data for the City of Toronto during the period January 1992 to June 1998.
It is estimated that a third of the world's population is infected with Mycobacterium Tuberculosis, the organism causing
tuberculosis (TB). These individuals face a 10% lifetime risk of developing TB disease. Each year, 10 million people
become infected and 3 million die from TB worldwide, prompting the World Health Organization to declare TB a "global
emergency" in 1993. The experience of New York City demonstrates that the disease can be effectively controlled with
improved TB programs, as a result of increased resources (see Figure1). Unfortunately in many countries beset by
economic disadvantage, political turmoil, the HIV epidemic and increasing TB drug resistance, very high disease rates
In Toronto, between 450 and 500 new cases of TB occur annually, comprising 25% of all cases in Canada and 60% of all
cases in Ontario. The number of cases per year has remained quite stable. TB incidence in Toronto is three times higher
than the provincial rate (20 per 100,000 vs. 7 per 100,000) (see Figure 2) and almost six times the goal set out in the
Mandatory Health Programs and Services Guidelines (3.5 per 100,000).
From January 1992 until June 1998, 78.2 % of all TB cases occurred in the former municipalities of Scarborough, Toronto
and North York. During this period, Scarborough and the former City of Toronto had declines in annual cases of 17.9% and
26.5 % whereas North York had an increase of 19.4%. The City of York also experienced an increase of 43.5%. This
redistribution of TB cases likely reflects changing immigration and settlement patterns across the city.
Since 1992, an average of 20 deaths each year in Toronto have been attributed to TB. However, preliminary results from
1997 indicate that there were 28 deaths in that year. This increase may reflect an increase in drug-resistant TB. The age
distribution of TB shows few cases under the age of 15, the highest peak between 25-44 years of age, and a second smaller
peak after age 65 years of age (see Figure3).
Since 1992, 16% of TB organisms with a known drug sensitivity pattern have been found to be resistant to one or more
antibiotics. Drug resistance prolongs infectivity and increases the risk of transmission to others since routine therapy often
fails to eliminate the organism. Treatment modification is often required, sometimes involving drugs that are 100 times the
cost of routine antibiotics. Since Isoniazid (INH) and Rifampin are the mainstay of TB treatment, greatest concern occurs
when resistance is present to both these drugs, creating multi-drug resistant TB (MDR-TB). In Toronto, 46 cases of
MDR-TB have been detected since 1992, or 2.1 % of all TB cases between January 1992 and June 1998. This is more than
double the national rate of MDR-TB, which is less than one per cent.
For TB cases reported in Toronto residents between January 1992 and June 1998, the three major risk factors were:
(i)Birth in a country where TB is endemic;
(ii)Underlying HIV infection; and
(iii)Impoverished social conditions (e.g. low income, underhoused).
(i)Birth in a country where TB is endemic
During this period, 87% of TB cases in Toronto occurred among people born in a country where TB is endemic. This is
hardly surprising given the prevalence of TB infection worldwide. Migration and relocation are significant stressors which
can weaken individuals' immune systems against TB. This is substantiated by the fact that 53% of these cases were
diagnosed within five years of their arrival in Canada, likely due to stress related to settlement and integration, as well as
lack of access to basic health prerequisites such as affordable housing and employment.
During this time, eight countries in the Far East, Southeast Asia and Sub-Saharan Africa contributed 68% of all
foreign-born cases. These same countries contributed 46.6 % of recent immigrants to Canada (Census 1996). Of all foreign
born cases of TB, 17.3% were drug resistant as compared with 7.8% of cases born in Canada.
(ii)Underlying HIV Infection
HIV infection poses the greatest risk for the progression of TB infection to disease. From January 1992 to June 1998, 103
cases of TB (3.4% of cases) occurred among individuals who were co-infected with HIV. Forty-three were born in Canada
and 60 were born in a TB endemic country (Figure 4).
The majority (88 %) were male and the mean ages were 37.4 years among males and 31.7 years among females. The
presentation of TB disease in those with HIV/TB coinfection differs from that of HIV negative TB cases. In the former,
disseminated TB was reported in 9%, compared to 1% among HIV negative individuals; as well, 27% of HIV positive
cases had lymph node disease compared to 21% of cases without HIV infection. The non-typical presentation of TB among
HIV infected individuals renders the diagnosis of TB more challenging for health care providers; this can lead to delays in
treatment, poorer prognosis and prolonged TB transmission.
Among TB cases where resistance patterns are known, 18% of HIV/TB cases had resistant disease compared with 16% of
HIV negative cases. This difference, though small, is significant and of concern because 9 of the 16 (56.3%) HIV/TB cases
with resistance had multi-drug resistant TB (MDR-TB) while only 10.8% of HIV negative cases with resistance were
MDR-TB. Another worrisome feature was the much higher case fatality rate among HIV/TB cases - 22.3% compared with
3.9% among HIV negative TB cases. Worldwide, TB accounts for almost a third of AIDS deaths.
(iii)Impoverished Social Conditions
Tuberculosis remains a disease of the socially disadvantaged. From January 1992 to June 1998, 105 (29.0 %) of the 362
Canadian-born cases were low income, homeless or addicted to alcohol and/or drugs. Unfortunately reliable socioeconomic
data for foreign-born cases is not available.
Currently, 2-3% of all TB cases in Toronto occur among the homeless or underhoused. Based on results of TB skin test
screening, 30-40% of the homeless in Toronto are known to be infected with M. tuberculosis. These individuals are at high
risk of progressing to active TB because of reduced immunity, high stress and other concurrent infections/diseases. Other
common risks among Canadian-born cases include close contact with a known TB case (13.5%) and underlying medical
illness such as cancer or diabetes (10.7%).
As this report shows, TB remains a significant health problem in Toronto. With continued high immigration from TB
endemic countries, one of the highest rates of HIV infection in Canada, and urban poverty, unemployment and
homelessness, continued vigilance is required in TB prevention and control. Program recommendations needed to meet this
challenge were highlighted in the January 1999 service harmonization report to the Board of Health.
Dr. Barbara Yaffe
Director, Communicable Disease
and Associate Medical Officer of Health
Toronto Public Health
Dr. Sheela V. Basrur
Medical Officer of Health