Ori
g
inal ArticlePROBLEMS IN ESTIMATING THE BURDEN OF
PULMONARY TUBERCULOSIS IN INDIA: A REVIEW

M.S. Krishnamurthy*

(Received on 5.2.2001, Revised version received on 2.7.2001, Accepted on 9.7.2001)

Summary :It is generally agreed that there is need for developing an acceptable estimate of the tuberculosis problem in
India. Estimates obtained by the National Sample Survey have been found to be deficient for the purpose of enabling
rational allocation of resources and evaluating efficiency of anti-tuberculosis programmes. The WHO commissioned a
study on the subject and subsequently published a review of the global burden of tuberculosis, in which the Indian situation
was also considered. The Government of India also formulated a Committee in 2000 to address this problem. The author
reviews the estimates so far obtained.

Burden of pulmonary tuberculosis - the current corresponding to the population escalation taking
estimates place in the country.

For developing an appropriate strategy for
combating tuberculosis in the country, it is necessary
to obtain a precise estimate of the disease in the
community. The process of estimating it for as large
and diverse a country as India is not only difficult,
but is also expensive and time consuming.

It is common knowledge that the nation

situation could result and this would require
measurement. It is, however, open to question how
precise the estimate for the disease should actually
be to make it amenable to measurement. On the one
hand, we are made aware by Chakraborty, in a recent
communication
1
, and even in an earlier paper
2
, that
he had found the available data in India unsuitable
for efficacy and efficiency evaluation exercises. On
the other hand, an editorial in the Indian Journal of
Tuberculosis (IJT) suggests that ideals (in estimating)
* Health Scientist, Bangalore

Correspondence: Mr M S Krishnamurthy, 2315, 21st Cross, Banasanhai II Stage, Banglore 560 0070

The Indian Journal of Tuberculosis

194

M.S.KRISIINAMURTIIY
need not be pursued, as long as practicable estimates

samples from X-ray abnormals, eight samples were
examined in a study by the NTI, in order to arrive at
an estimate of the total bacteriological case load in a
given community
5
. Further, in another study at the
NTI, instead of the conventional X-ray reading
technique, an innovative system of interpretation of
the radiographic abnormalities along with a series of
follow-up X-rays and other examination findings,
was relied upon in order to get a correct estimate of
the initially radiologically active cases in the
community
6
. This technique of X-ray reading was
termed as Joint Parallel Reading (JPR). From the
former study, it was found that the yield of
bacteriologically positive cases was more by 37% in
multiple sputum examination method ; and in the
latter study the JPR method of reading showed that
only 22% of the radiological cases, classified as active
cases by conventional method, could actually be
confirmed as truly active TB cases. Apart from the

JPR method, there is other amply corroborated
evidence to support the finding of an over-estimate
of radiologically active cases as obtained through the
method of conventional X-ray reading. In longitudinal
surveys carried out by the NTI, the prevalence of
these cases was 10.6 per 1000 in I survey & 6.8,

rays
12
. In more recent times, Chakraborty et al found
that the estimates of prevalence of disease made by
the use of either of the screening tools should be the
same, if the symptom elicitation was made either by
a social investigator or by a senior experienced worker
in the field of tuberculosis
13
. These significant
findings influenced many of the tuberculosis workers
to carry out similar surveys in different areas of the
country, beyond the seventies. They carried out these
surveys in relatively larger population groups, from
which valid statistical estimates of prevalence of
disease could be computed. The findings of such
surveys, with and without applying the coirection
factor as suggested by Gothi et al
12
, and the findings
of two major X-ray surveys are given in Table 1.

The Indian Journal of Tuberculosis

ESTIMATING THE BURDEN OF PULMONARY TUBERCULOSIS IN INDIA

195

Table 1 : Prevalence of tuberculosis in India according to screening tools used
10

Significance of
the result in
relation to NSS
at 95% confiden-
ce limits (for
corrected rate)

National Sample

Survey(NSS)

1955-582,00,429

X-ray5.4
(5.05-5.69)

N.A.
Chengalpattu
(Tamil Nadu)
3.6

P<0.05Raichur
(Karnataka)1988-8940,496Symp8.8
(7.89-9.71)13.2
(12.87-13.53)P<0.05Karhal Block

elicitation. For the surveys carried out using symptom
elicitation as initial screening, the respective rates of
prevalence of disease as observed and as computed
after applying the correction factor (as suggested
by Gothi et al
12
) have been furnished in col 5 & 6.
The observed prevalence rates, as well as those
obtained after applying the correction factors, were
found to be statistically different (P<0.5) from those
observed in NSS. In the light of significantly different
prevalence rates found in different surveys, beyond
the seventies, the assumption that the prevalence of
disease is uniform a l l through the country,
(“distributed ubiquitously” as suggested in Forum
under Editor replies
3
), may not be correct.
Unfortunately, and strangely at that, the same
hypothesis developed during the NSS, receives
support of the scientific community, even to this day
4
in the face of scientifically analysed data pointing

otherwise. Stranger still is the fact that the same
hypothesis is still being followed even by the NTI
for the purpose of monitoring the programme,
nationally. ARI studies currently being undertaken
by the NTI all over the country, are likely to throw
more light on this aspect, and would hopefully resolve

10
. This was followed by the work by
Christopher Dye et al in 1999, as a part of the global
exercise and expressed as a consensus statement by
the WHO Geneva
14
.

It was against this background, that the
Government of India convened an 'Expert
Committee' in 2000 and assigned them the task of
estimating the burden of TB in the country
4
. The

Committee reviewed all the available data, including
the estimates made by Chakraborty and Christopher
Dye. It identified the various surveys carried out in
the country which had followed similar investigation
procedures. The average both sexes all ages rates
from these surveys were standardised on the basis
of the observed prevalence rates in different age and
sex groups of each survey, with the projected
population structure of 2000. A weightage was
given for the size of the population covered in each
survey to estimate the burden of disease in the
country.

Table
2: Prevalence of tuberculosis cases in India (average rate/number) for standard population

ConventionalPrev of C+ cases @ 4.0 in 5+ age326516321,3051:3estimate

Grou
p
Prev. of X+ cases
@
16.0 for 5+

13

44.9% of
C+
)Chakraborty

Prev. of C+ cases @ 6.0

4,897

2,448

1,958

1:3

A.K.
10
Prev of X+ cases @ 3.0

2,448

-

2,352Tamil Nadu

in 1 0+ a
g
e
g
rou
p(@
52.23% of(
estimates made

(
1968-70
)
I Surve
yC+ cases of

1,865selected for

in 1 0+ a
g
e
g
rou
p(@
6 1.67%the BCG trial)

(1984-86) V I I Surveyof C+ cases)Population considered: 960,178 ( in thousand) as per Christopher Dye et al
14
C + : Bactenologicallv positive cases (culture / culture and smear positive)
X+ : Rad iol ogically active patients

detail. Since the conventional estimates, which were
so far followed by the NTI, had not taken cognizance
of the findings of its own studies in respect of
additional yield of 37% of the culture positive cases
by multiple sputum examination, and the likely fact
of a confirmation of only 22% of the radiological
cases arrived at by following the conventional method
of X-ray reading, the estimate of 32,65,000
bacteriological cases, could be an underestimate.
On the other hand, the number of 1,30,60,000 taken
as the burden of radiologically active cases is a gross
overestimate. To consider 4.0 and 16.0 per 1000 as
the prevalence of bacillary and X-ray active cases,
respectively, does not seem to be correct, on the
available evidence.

From Table 1, it can be seen that the
prevalence rate of bacillary cases is not uniform all
through the country. In support of this, it may be
stated that, even under NSS, pockets of high
prevalence like Calcutta slums were found.
Therefore, how far it is rational to consider an uniform
prevalence for the entire country, given its diverse
socio economic scenario and the sheer size, is
anybody's guess. Besides the differences by space,
there are changes in time as well, as seen from the
NTI and TRC studies in rural Karnataka and

Tamilnadu. NTI, from its own studies had found
that the proportion of smear positive to total number

Dye et al to estimate of prevalence of bacteriological
cases @ 5.05/1000, which was possibly less
representative in the context of the whole country.
Further, the observed proportion between incidence
and prevalence cases in longitudinal study of the NTI
was 1:3 and this proportion was modified by Dye et
al as 1:2.7. The reason for this change requires an
explanation. Dye et al further chose to refrain from
estimating the prevalence of radiologically active case
load, the most likely and an understandable reason
for this being the lack of confirmation of such cases,
as brought out by JPR study of the NTI and also by
TRC studies, as explained above.

A look at the estimates of Chakraborty
10,11

the other hand, shows that he has refined the
estimates of bacillary as well as radiologically active
cases, based on earlier NTI studies on multiple
sputum examinations and JPR technique of X-ray
reading. It is true that when the estimate of
bacteriological cases is increased, with the
assumption of investigation of eight sputum samples,
there would be considerable decrease in radiological
cases, as most of these cases, could be represented
as bacteriologically positive cases, with any of the
eight sputum sample becoming positive. Thus, the
decrease may not appear illogical at all, and is no


wherein the initial investigation tool was 'symptom
elicitation' made the estimate less representative in
the country's context. Further, and more importantly
at that, failure to take cognizance of the findings from
NTI studies on multiple sputum examination and JPR
technique of X-ray reading, as done by Chakraborty,
is bound to lower the estimate of bacillary cases and
raise the estimate of radiological cases. These appear
to be serious flaws in the estimate.

Though the proportion of smear positive
cases out of the total bacteriologically positive cases
was found to vary from 44% to 58% in the first five
longtudinal surveys
7
(it was as low as 15.8% in 1984
survey
15
), by the NTI and about 48% in the TRC
study
17
, the expert committee's decision to consider
the proportion at 68% does not appear logical. This
unreasoned stance makes the estimate of smear
positive cases unreasonably high and unacceptable.

CONCLUSION

With the renewed concern for tuberculosis,
globally and in Ind ia, there is an augmented

of sputum samples (two) customarily examined in
surveys, and the over-diagnosis due to the X-ray
reading technique. The revised rates as worked out
by Chakraborty in the Report commissioned by the
WHO, had made good this deficiency
10
. However,
he had not taken into consideration the fact of
demographic changes occurring due to age and sex
variations in the population with time. Both the reports
by Chakraborty as well as by Christopher Dye, as
brought out by the WHO, had not taken into
consideration the surveys carried out on the basis of
symptom elicitation in the population, and thus had
missed one of the essential features of the
epidemiological situation in India, as shown in Table
1, that is, the prevalence rates were different from
area to area and not similar, as was their hypothesis.
In giving an average prevalence rate for the country,
they could thus be on untenable grounds. However,
this deficiency may seem to be offset to an extent
by the ranges they had chosen to give for each of
the estimates
10,14
, thus admitting the fact of disparate
rates from area to area. Even then, it could be a
debatable exercise to present an average for such
rates, as were found to be lying outside the 95%
confidence limits, as in this case. It appears to be as
far fetched an exercise as presenting an average rate

specimens examined, as well as on the over-diagnosis
inherent in the X-ray reading technique. Moreover,
they had chosen to consider the proportion of smear
positive cases to be over 60%, for which there is no
support from the available data. Thus, the
prevalence rates given above by different groups
were different from each other, and each with
obvious lacunae in estimating procedures. To
be meaningful, these differences need to be
resolved, as they are bound to influence the
decision of health planners for allocation of funds
and for monitoring of the programme.

REFERENCES

1. Cliakrahorty AK, Epidemiology of TB ; Some ifs and buts,
IndJ Tub, 2000,47, 184

2. Chakraborty AK, TB situation in India: measuring it through
time, IndJ. Tub,
1993,40,215

3. Editorial, On estimation of burden of TB in India,
Ind J.
Tub,
2000, 47, 127.

4. Editor replies,
Ind J. Tub,
2000, 47, 186


12. Gothi et al, Estimation of prcv. of bacillary TB on the basis
of Chest X-ray and / or symptom screening, Ind J Med
Res, 1976,64, 1150.

13. Chakraborty AK et al, Prevalence of pulmonary TB in a
peri-urban community of Bangalore under various methods
of population screening, IndJ. Tub, 1994, 41, 17.

14. Dye, Christopher et al, Global burden of TB; estimated
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Aug 18, 1999,282,677.

15. Chakraborty et al, Prevalence of TB in a rural population
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16. Chakraborty et al, Tuberculosis situation in a rural
population of south India ; 23 year trend, Tubercle and
Lung Dis, 1992, 73,213

17. Tuberculosis Research Centre, Chennai, Trends in
prevalence and incidence of tuberculosis in south India, Int
J Tuber Lung Dis, 2001, 5(2), 142
The Indian Journal of Tuberculosis