PROBLEMS IN ESTIMATING THE BURDEN OF PULMONARY TUBERCULOSIS IN INDIA: A REVIEW pot

It is common knowledge that the nation wide sample survey carried out by the Indian Council of Medical Research ICMR in 1955-58 NSS, followed by several similar surveys conducted at the

Original Article

PROBLEMS 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

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

wide sample survey carried out by the Indian Council

of Medical Research (ICMR) in 1955-58 (NSS),

followed by several similar surveys conducted at the

National Tuberculosis Institute, Bangalore (NTI),

New Delhi Tuberculosis Centre and the Tuberculosis

Research Centre, Chennai (TRC) had provided the

basis for estimating the prevalence of tuberculosis

in India On an average, the same was taken to be

4.0 and 16.0 per thousand for bacteriological (C+)

and radiologically active tuberculosis cases (X+)

respectively Although the tuberculosis situation and

the prevalence rates were considered to be static in

time, as per the findings of several of the studies

carried out in India, the absolute number of cases in

the country had to be constantly revised upwards,

The case for revision of estimates

The global resurgence of tuberculosis, especially in the context of Human Immuno- deficiency Virus, has created an unprecedented awareness for tuberculosis in recent times Several international bodies have, as a result, involved themselves in tuberculosis control with an intensity never evidenced before The question, however, which has been disturbing the intervention-strategists

is how to evaluate changes in tuberculosis situation, following the implementation of the control measures requiring investment in money and manpower Evidently, some kind of change in the tuberculosis 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 communication1, and even in an earlier paper2, 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

were taken as ideals3 It is also understood from the

editorial published elsewhere in the same issue of

the IJT, that amidst this controversy, the Govt of

India had arranged a 'consultation' at the NTI,

Bangalore for resolving some of the issues and

providing an estimate of the tuberculosis burden in

India4 It is presently intended to discuss some of

the problems here, in arriving at the estimate of the

tuberculosis burden in the country

As has been brought out in an earlier para,

the rates of both bacteriological and radiologically

positive cases were more or less considered to be

unchanged in time so far In the seventies, the NTI

had attempted to refine both the prevalence of

bacteriological and radiological cases5, 6 This, in the

first place, was in recognition of the limitation of the

yield of bacteriological cases by the investigation of

only two samples of sputum from the X-ray

abnormals in a survey The limitation of X-ray

interpretation by two independent X-ray readers,

followed by an umpire reader, was also a factor to

consider in estimating the radiologically active

disease Instead of investigating only two sputum

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 community5 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

community6 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, 4.2 & 4.3 in II, III & IV surveys7 Further, in the Chengalpattu study, while the observed high prevalence of bacillary cases was at 10.68 per 1000, the prevalence of radiological cases was 4 29 per

10008 The New Delhi Tuberculosis Centre survey also had shown substantial reduction of the X-ray positive case prevalence in later years9, ostensibly due to an improved interpretation of X-ray shadows, probably influenced by the results from the NTI study

on the fate of X-ray cases diagnosed in a survey (JPR study), available by then It is strange that these significant findings on the JPR study were not incorporated by the NTI in estimating the burden of disease, even to this day, till Chakraborty in his report

to the WHO used them to present a set of new prevalence rates for the country10,11

In the seventies, NTI had realised the need

to modify the expensive conventional survey technique by adopting alternative cheap investigation procedures In this pursuit, NTI used 'symptom elicitation' as the initial screening tool, instead of X- rays12 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 tuberculosis13 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 al12, 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 used10

Survey Period

of survey Population covered Initial screening

tool

Prevalence

of C+ cases (11 respective

of smear result)

in 15+ age group

Prevalence after applying correction factor

Significance of the result in relation to NSS

at 95% confiden-

ce limits (for corrected rate)

National Sample

Survey(NSS)

1955-58 2,00,429 X-ray 5.4

(5.05-5.69)

N.A

Chengalpattu

(Tamil Nadu)

1968-71 2,04,624 X-ray 10.8

(10.36-11.26)

N.A

Wardha

Raichur

(12.87-13.53) P<0.05 Karhal Block

Morena District

(Madhya Pradesh)

(7.87-11.52) 14.6

(13.89-15.21) P<0.05

(Range for 95% confidence limits given in brackets) C+: culture/ smear positive cases Symp: Symptoms

It can be seen from Table 1 that the NSS

and Chengalpattu surveys were carried out using X-

rays as initial screening tool and for the rest of the

surveys, the initial tool of investigations was symptom

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 al12) 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 all through the country,

(“distributed ubiquitously” as suggested in Forum

u n d e r 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 day4

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 the issue

Attempts at redefinition of the problem in recent times

As has been brought out in an earlier paragraph, that warning signals in respect of the tuberculosis situation globally have been taken seriously and there are now attempts to work out the global burden of tuberculosis, including India Inspite of efforts to underplay the need and the method used for revising the estimate for the country3,4, there have been two attempts from the WHO Geneva, to analyse the problem and arrive at

as precise an estimate as possible, in the Indian context Under the auspices of the WHO, Chakraborty re-estimated the burden of disease in

The Indian Journal of Tuberculosis

the country, updating the technique followed

heretofore, by incorporating the findings of JPR and

multiple sputum investigation studies as explained

earlier10 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 Geneva14

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 country4 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

Individual/

Group

PievalenceforC+/X+

cases (per 1000)

No of C+/X+

(in , 000)

No of Sm+

Potential (annual) of case finding under NTP (No.)

Ratio of Incidence: Prevalence

Prev of X+ cases @ 16.0 for 5+ 13,060 age group (Sm+ cases 50% of C+)

Dyeetal1 4 Prev of X+ cases not estimated) (44.9% of

C+)

A.K.10

observed rates below as 30%)

in 1/3 of the

Population considered: 960,178 ( in thousand) as per Christopher Dye et al 14

C + : Bactenologicallv positive cases (culture / culture and smear positive)

X+ : Radiologically active patients

Sm+ : Smear positive cases

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ESTIMATING THE BURDEN OF PULMONARY TUBERCULOSIS IN INDIA 197

Based on the above exercise, one has now

access to a fresh set of estimates of the burden of

tuberculosis in the country, as of today It serves to

provide one standard average prevalence rate,

corrected to represent the current Indian population

structure, age and sex-wise This would eliminate

the confusion created by different rates put forward

by painstaking work by a number of individuals and

agencies Table 2 provides information on the

estimates of prevalence obtained from various

sources, compared to that arrived at by the expert

group convened by the Government of India (2000)

Information is available in the Table on the estimate

of prevalence rates followed by the individual / groups

and the computed number of culture and smear

positive cases for a standard population

Suitability of the newly computed estimate :

opening Pandora's box?

The estimates given in Table 2 and their

suitability for use require to be discussed here in some

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

of culture positive cases as observed in I, II, III &

IV surveys had changed from about 50% to just about 15% in the span of some 22 years15 Moreover, there was an observed change in the ARI

as well for the given area16 The TRC study in rural areas of Tamilnadu has also shown a long-term and sustained decline in the disease rates with time17 However, no such change has been observed in the urban population studied in New Delhi9 Thus, to consider a uniform prevalence rate for average is just an untenable hypothesis, both for space as well

as time for this country

A look at the estimate arrived at by Christopher Dye et al14 suggests that they had taken into cognisance the findings of most of the surveys wherein X-ray was the initial screening tool They had chosen to ignore the findings of surveys, wherein the initial screening was 'symptom elicitation' Disregarding the findings of these surveys had led 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 Chakraborty10,11 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

The Indian Journal of Tuberculosis

doubt affected by the use of evaluated data from

field studies However, it could be seen that he had

chosen not to consider the fact of changes occurring

in age, sex structure of the community In all this,

he had followed the hypothesis of no change in

prevalence rates over time, calculating the absolute

numbers on the basis of current population size,

without taking into account the age-sex changes in

the population, affecting the prevalence rate The

higher and lower prevalence rates, found in other

surveys are no doubt represented by him as ranges,

with an arbitrary midpoint giving the average

The exercise made by the Expert Committee

convened by the Government of India (2000) is

unique indeed, attempting the standardisation of

observed prevalence in different age groups with the

projected population of 2000 Weightage was

accorded for each of the surveys, based on the

populations investigated in each survey for finally

arriving at an estimate of both C+ and X+ cases

However, not considering the findings of surveys

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 surveys7 (it was as low as 15.8% in 1984

survey15), by the NTI and about 48% in the TRC

study17 , 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 India, there is an augmented

intervention effort for tuberculosis control In view

of this, there is a perceived need for developing

an acceptable estimate of the problem, to enable

the programme planners to allocate resources,

as well as to evaluate the efficiency of programme delivery The available estimate obtained

from the NSS has been found deficient for these purposes The WHO had commissioned a study of the tuberculosis situation in India based on available data, published under its technical reports series10 They had followed this up with publication of a review of the global burden of tuberculosis, in which the Indian problem was also estimated14 Later still, the Government of India had formulated an expert committee in the year 2000, which had deliberated

on the issue and suggested a revised set of prevalence rates for the country In this paper the above estimates have been reviewed

The conventional rates of C+ and X+ disease

at 4.0 and 16.0 per thousand on the average were not acceptable, since they had not taken into consideration the under-diagnosis due to the number

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 deficiency10 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 estimates10,14 , 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

of pulmonary tuberculosis, which would be globally applicable To the credit of Chakraborty, it can be said that though he had presented an average rate

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ESTIMATING THE BURDEN OF PULMONARY TUBERCULOSIS IN INDIA 199

for the country10, he also found it indefensible1 It

appears that he had compromised on the rates in

vogue, even as he found them inappropriate Further,

the reason for the ratio of incidence : prevalence, as

shown to be 1:2.7 by Dye et al, is not justified on the

basis of available information14

The rates, as worked out by the Government

of India expert group, suffer from the same lacuna

of not considering the results of surveys on the basis

of symptom elicitation and concluding on an equal

average prevalence rate for the entire country The

latter had also erred in disregarding the overwhelming

evidence of under-diagnosis of bacteriological cases

in the surveys, related to the number of sputum

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

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