Tuberculosis in Canada
Tuberculosis is a severe bacterial infection of the lungs and other
in three people in the world are infected with Tb.
million deaths occur each year from infection.
is related to the length of exposure to and infectivity of the contact
Infection is contracted by droplet nuclei from coughing.
bacteria are then ingested by alveolar macrophages in the lungs
causing the primary infection.
then spreads through the blood (hematogenously) and becomes a latent
Active Tb disease will develop in 10% of these latent infections
(usually this occurs within 2 yrs in 80% of those who do develop
lungs are most commonly infected (about 50%).
x-ray cavitations, caseation, and fibrosis can be seen.
pulmonary TB is infectious to others.
direct stain for acid-fast bacilli diagnoses active TB and this
is confirmed by culture.
X-ray will show lung infection.
of the worst types of Tb infection occur more in children under
5 yrs and are miliary (generalized infection) and Tb meningitis.
Latent Tb by definition is symptomless and is diagnosed with
the tuberculin skin test (the Mantoux test) where tuberculin protein
is injected intradermally on the forearm to see if that person has
been sensitized to tuberculin in the past (either with a prior exposure
to the disease or vaccination with BCG).
techniques may be used in the future.
of latent Tb can be months on anti-tuberculosis drugs.
Tb is poverty related.
soon as living conditions improve the Tb incidence goes down.
and AIDS can accelerate the symptoms and progression of Tb.
increases the progression of Tb from 10% of latent infections towards
active per life to 10% per year of those affected.
the rise of HIV Tb has risen and is expected to rise further.
There is an under appreciated risk to the traveler of Tb infection
but little hard data on this.
are reports of Tb outbreaks among airplane passengers who had sat
next to heavily infected individuals who were actively coughing
during long flights.
are at risk to exposure.
are outbreaks of TB, especially among air travel although this is
felt to be very low.
Risk to travelers of Tb exposure can be expressed from the rate
of Mantoux skin test conversions from negative to positive indicating
that exposure has occurred.
A Peace Corps study showed 15 per 1000 traveler years skin test
another study health care volunteers had a conversion rate 7.9 while
tourists had a rate of 3.5.
and long term tourists have a risk of Tb that becomes similar to
the host country (1-3 %).
The risk of catching the disease is relative. In order of frequency
diseases are; HEPATITIS A (0.3%-2%) > LATENT Tb INFECTION > HEPATITIS
B > ACTIVE Tb > TYPHOID (~0.003%)> MENINGITIS> CHOLERA (1 in 500,000)
per travel month
TB PREVENTION FOCUSES ON:
1) Avoiding exposure.
2) BCG vaccination.
3) Identifying and treating latent Tb infections.
BCG (Bacille Calmette-Guerin) vaccination is a live attenuated vaccine
of Mycobacterium Bovis (cow tuberculosis) which protects
against disease but not infection.
will induce Tb sensitivity but not infection.
compare different effectiveness and opinions vary from country to
country from 0-80%.
better - designed studies it appears to have a more proven benefit.
to the equator studies have shown less protection.
does protect against the military and meningeal Tb infectionsin
children under 5yrs..
is thought to be about 10-15 yrs.
used in the past with high- risk population (native children and
military personnel) it is not presently given routinely in Manitoba
except for high risk Aboriginal children.
In some countries where it is given it is administered at least
6 wks before travel.
to its use are: immune suppression, any HIV infection regardless
of their CD4 counts, and a positive Mantoux test.
include having an abscess formation at inoculum site.
BCG may be considered in:
1. If patient is under 5 years and at high risk.
are more likely to develop meningeal or military Tb - 2 conditions
that are prevented by the vaccine.)
2. Poor compliance for follow up i.e. They never return to
get their Mantoux done properly or would be noncompliant with Tb
3. Individual would be at risk for severe side effects from
the BCG is infrequently administer outside of Northern Communities.
The Mantoux test consists of injecting 0.1 ml of purified tuberculin
injection site must be read by an experienced doctor or nurse 48-72
protein is not infectious and there is no risk of acquiring Tb from
immune system will recognize the tuberculin protein if that person
has been sensitized (either be exposure to Tb or with the BCG vaccine)
and mount an immune response at the injection site (which becomes
red and indurated).
Local guidelines should for interpretation should be followed, as
tuberculin doses are not universally standardized.
Manitoba 10mm of induration is felt to be a positive test.
of this test may be affected by insulin dependant diabetes and pregnancy
although these people should still be tested if indicated.
There also exists a booster effect from having a recent Mantoux
test if given recently.
a 2 step Mantoux test can detect this.
test checks to see if a boosting effect occurs from the first injection
of tuberculin rather than because of true exposure to tuberculosis.
The manitoux test is done once and then again 1-3 weeks later to
see if a boosting effect takes place
If a boosting effect does take place then this can be noted and
compared with that patients Mantoux when checked again after their
By doing this 2- step test there is increased sensitivity for catching
new cases of Tb and treating them soon to prevent further contagion.
Individuals who had been vaccinated with the BCG vaccine will have
a positive Mantoux although if vaccinated in their first year of
life they may be Mantoux negative.
If a BCG has been done in the past it is recommended to do the 2
Individuals with weakened immune response may show anergy or the
inability to mount an immune response against the Mantoux test and
will be false negative. (This ironicall includes HIV infected people
who are also at higher risk for Tb).
TREATMENT OF POSITIVE CONVERSIONS (New Latent Infections)
All new suspected conversions should be referred to a local Tuberculosis
Treatment Program for further assessment and follow-up. Anti-tuberculosis
drugs need to be taken for months and patients need to be followed.
1. Long- term travelers have a risk for Tb
2. BCG may be recommended for high- risk travelers (although
not in Canada).
3. Serology may replace skin tests in future, which could
aid in detection much easier.
4. Newer vaccines unlikely to come out in near future.
At present the best way to control Tb is to promptly treat new cases
and have people educated in high risk situations.
Source: 8th ISTM Scientific Assembly 2001,Yellow
Book 2001, The CDC Pink Book 2000.