MFCM043: The Rationale of TB Control Programme - Epidemiological Perspective.pdf · medico friend circle

MFCM043: The Rationale of TB Control Programme - Epidemiological Perspective.pdf

Media

extracted text: cOv'wuNnv he*'-™ C£LL

The Rationale of

T.B.

Control Programme

ffiidemi olocji ca l_Perspec ti ve

Koramonga'a

Banga'ot*-5®003*
ladia

Prepared by "ARCH" Mangrol
for 1985 GVHA Convention.

Like all other infectious diseases, T.B. has its oiun
peculiarities and characteristics,
Unless this is firmly grasped,
the adequate understanding of T.B. Control programme is impossible.
One of the ways these peculiarities manifest themselves is to
be seen in the fact that only in T.B. and Leprosy (which in many
respects is like T.B.) the control of the infection in the
community is very closely linked with treatment of individual
cases.
In all other infections, treatment of individual cases
either has no place in control programme or has marginal role
in the over-all strategy of the control programme.
In T.B.,
treatment of individual cases dominate the strategy almost
completely.
This may create a misunderstanding in our minds
that T.B. control programme is, after all, curative medicine
with no preventive component.

For a group that is committed to primacy of prevention
over cure, this state of affair may no"^ be intuitively satisfactory.
This note is also an attempt to dispel such misgivings, if they
are there.
(I)

T. B.

infection and disease:

T.B. is unique amongst all the infectious diseases in
that its germs, having entered the human body multiply in
the lungs and- various organs, producing what is called
infection, but not overt disease in all the victims in
whom they have managed to enter.
The Tuberculous germs,
thereafter, may be overcome by the body’s defence system
and eliminated completely or may be forced to go into a
dormant state.
In a small proportion of cases where the
body’s defences are overwhelmed, Tuberculous disease is
manifested, which is the only portion of the’total cases
of T.B. infection that is apparent to our day-to-day common
perception.1

The things get a bit more complicated, because the portion
T.B. infection in a community, which is dormant can get
reactivated any time during life, producing the overt
disease T.B..
This gives T.B. infection an extraordinarily
large variability of incubation period. A person once
infected, and in whose body the germs lie dormant, can
become diseased anytime during life.
Jhe_spread_of_ T. B^^infection:

* The spread of the T.B. infection occurs by
transmission of bacteria mostly from person
to person and in some cases from cattle to
human being, (bovine T.B.).
The spread from
person to person occurs almost exclusively
through air.

1 In a situation like ours there are 300 per 1000 who are infected
but only 4 to 6 per 1000 who are diseared

2

★ All the infected persons cannot excrete
the germs in the air.
Only those
infected and who have T.B. disease of
the lung and who are actively coughing
out the T.B. germs in the sputum are
the ones who spread infection.
The
T. B. disease of organs other than the
lungs (extrapulmonary T.B.) occurs
through blood following primary infec
tion.
The proportion of extra pulmonary
T.B. disease is quite small compared to
lung T.B- disease.
Extra pulmonary
diseases are, therefore, of little
consequence in so far as spread of T.B. .
infection is concerned.

Two important points, from the point of
T. B. control may be made here.
(a)

Only lung cases who are coughing
out T.B. germs in their sputum
(Sputum positive- open cases of
T.B.) are responsible for spread
of infection in a community.

(b)

These open cases of T.B. arise at
different intervals and at different
rates from those who are infected
wi th T.B. germs.

★ T.B. infection is a very slow infection,
A prolonged
i.e. it spreads very slowly.
contact with a case of T.B. is necessary
which explains concentration of cases in
families.

(II)

Factors responsible for the spread of infection in families;
(a)

Infection in family contact is closely related to
the extent of disease and sputum positivity of the
source case.

(b)

Next in line is overcrowding- measured as cubic
feet per person and subjective assessment of intimacy
of contact -.

(c)

Surprisingly enough,the household income purse is
not of much importance, while what household
furnishings the families purchase with their income
seems to be a factor of considerable significance.

(d)

Contrary to our expectations, nutrition is not a
factor of any importance in the spread of infection.

(e)

Infectiousness of T.B. patients decline rapidly
by adequate treatment.
Thus a patient who is on
chemo-therapy stops infecting others although he
may still be sputum positive.
This is so because
germs in the sputum do not remain viable once the
chemotherapy starts.
This is, what is caJLled,
’Chemical isolation’ - an important point from the
point of view of prevention of transmission in
practical terms.

3

(HI)

Factors responsible for mahifestat ion of T.B. dis ease:

Contrary to T.B. infections where the risk factors are
extrinsic, the risk factors in the development of the
disease are largely intrinsic.

(IV)

__ -'l

(a)

Different infected populations develop T.B.
disease at very different rates. e.g., risk of
developing T.B. disease in Eskimos is 20 times
more than that in the infected, non-urban
Danish population.

(b)

Young, adult, infected women are at higher risk
of developing T.B. disease than young, adult,
infectedmales.

(c)

Housing, including overcrowding and ventilation,
is of no importance.

(d)

Importance of nutrition is also of a peculiar
character.
Only those who weigh 10% or more of
their average expected weight are at lower risk
of developing T.B. disease.
Those with lower
weights have proportionately increased rate of
T.B. di sease.

Strategy of T.B. Control in the light of Epidemiological
Insi ghts;
Theoretically to control the infectious disease in a
community the strategy should be directed at s

i)

source and reservoir of the infectious
germs;

ii)

the routes of transmission of the germs to
the susceptible human beings via media like
water, food, air, insects;

(iii)

strengthening the defence mechanisms of
susceptible individuals against .the invading
germs, e.g. - Vaccination

The most important components of T.B. control programme
are:

'and

i)

Case detection,

ii)

Case holding for the whole length of time
during which chemotherapy is instituted.
How does this strategy help control T.B. in
a community ?

UJe know that the germs of T.B. theoretically
are to be found in all the open cases of
pulmonary T.B., in all the cases of extrapulmonary T.B. and in all who are infected and
have T.B. germs lying dormant in their bodies,
which can become active any time during the
life in a most unpredictable manner and
produce the disease.
However the open cases
transmit the infection most and also T.B. germs

4

can be detected much more easily in the open
cases.
It is also true that the suffering and
death is to be found only in T.B. disease,
pulmonary or extra-pulmonary, and not in the
third category in which the germs are lying
dormant.
In the T.B. disease category, also,
overwhelmingly large proportion of the disease
is pulmonary T.B.
In practice, therefore, an attack against the
source of infection has to be confined to the
open cases of T.B. And as long as ths detected
open cases are treated adequately, they are
effectively removed from the most active part
of the part of infection in a community. And
this matters most.
This explains the emphasis
given in T.B. control programmes to case
detection and case holding.
This also explains
why case detection is most reliable by micro
scopic examination of sputum to detect T.B. germs
directly and unumportance of X-ray as a method
of diagnosis.
(Screening of ths chest is not
even worth mentioning.) This also explains the
apparent curative orientation of control
programme which, in fact, is the best available
means to check the transmission- the best
possible way to prevent T.B.
/(b)

The reason why T.B. control programme ignores
the classical, preventive measures like improving
sanitation housing etc. has also to do with the
peculiarities of its epidemiology.
Improvement
in housing, specifically reducing ths over-crowding
has an influencing effect on T.B. infection.
But, it cannot influence sufferings and deaths.
It also cannot have any influence on the clearing
of a huge backlog of existing infection in the
community which will continue to generate hundreds
of thousands of new cases of T.B. disease for many
decades to come.
It is also of secondary importance
in checking the transmission of the infection of
T.B. germs, when compared with the chemical
isolation of active cases of T.B. disease in a
family.
This, however, should not lead to an
interpretation that improvement in housing should
be outside the limits of the strategy of T.B.
control, as is the case to-day.
In fact, improve
ment in housing does not only affect transmission
of T.B., but also cuts down transmission of many
other infections. No community health movement of
some worth can drop the demand for the improvement
of housing for poor.

(c)

This brings us to the thrid component of strategy
of controlling infectious diseases in the community:
protection of all individuals against the infection
by vaccination. UJhat is the role of B.C.G. vaccine
in T.B. control programme ?

=□:x;o=

• 6th November 1985

Position: 2372 (2 views)