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We're really trying to make sense of TB in India

The WHO’s most recent Global TB Report reckons that probably over a quarter of the world’s annual new TB cases are occurring in India. Meanwhile, the official statement from the Indian government itself has been that TB will be driven into submission in the country by 2025.

Five years is an incredibly short time with TB, so we’ve taken a look back over the last few years (and much further back well) to get a better picture of what this aspirational idea might actually consist of and we’ve found very little by way of reassurance.

So how many TB cases are actually currently occurring each year in India?

All that can really be said is that there is a slightly better idea about this today than there was five years ago, but there’s still little to be too confident about and plenty of uncertainty. (There’s certainly serious concern about this among some experts). One thing we can report with confidence is the estimate that was reported most recently by the WHO: the number of incident new cases of TB in India in 2019 was estimated to be about 2.64 million.

These ‘incident’ cases (which are the numbers of new TB cases that are reckoned to occur each year) are always estimated because it’s unanimously accepted that, even in countries with low TB burdens, some cases always get missed. In India, expert-guessing this number has been the game for years but it’s well-known to have been problematic. There is therefore a further measure which helps build a better picture: the total number of new cases who are actually notified each year expressed as a percentage proportion of those who are believed to exist (the ‘case detection rate’ or CDR). Over the past few years this CDR has been variably estimated for India: quite low; then quite high; then lower again, and then (more recently) higher again. Between 2013 and 2014, for instance, it rose from 58% to 74%; between 2014 and 2015 it reduced back to 61%. Then for 2018 it was back up to 74%, and for 2019 it was 80%. (The overall global CDR, incidentally, was reckoned to be 71% in 2019 and there is little reason to believe that India’s is likely to be higher than this, as we’ll see).

To be fair, Indian notifications of new and relapse cases increased from an appalling 1.2 million in 2013 up to 2.2 million in 2019 (a 74% increase), and this included an increase of a quarter of a million just between 2018 and 2019. These significant improvements resulted from the belated introduction of a national policy of mandatory notification in 2012, and the rollout of a nationwide web- and case-based reporting system (called “Nikshay”), which facilitates the reporting of detected cases by care providers in both the public and private sectors.

Exactly because of this prevailing uncertainty (not just in India but all over the world) it’s universally agreed that the WHO’s ultimate goal should be “to directly measure TB incidence from TB notifications” with nearly all cases found and treated. Since that still remains a pipedream, the second best alternative is to estimate incidence from surveys which measure the representative ‘prevalence’ of TB across any country.


Prevalence is an epidemiological term that reflects the amount of disease that's actually ‘out there’ at any point of time (i.e. not just the new cases, but the ongoing prevailing cases that remain potentially infectious as well). Because tuberculosis is a slow-burning disease which takes years to pan out, the number of ‘prevalent’ TB cases is invariably higher than the ‘incident’ number – though this discrepancy should reduce if case detection improves of course. (This is totally the opposite, it should be noted, to fast-acting infectious diseases like Ebola - or indeed COVID-19 - when the prevalence is invariably lower than the incidence).

Prevalence can generally be assessed and calculated fairly reliably from a carefully designed ‘national TB survey’. This is when a typical cross-section of a national population is tested for smear-positive pulmonary TB disease after which the percentage that’s found positive is applied to the total population. It’s certainly not 100% accurate because not all variable factors can be ruled out (and there are a lot of them in a country like India), but it’s far better than expert guesswork (which is the next best alternative). What’s important to appreciate is that prevalence is the only way to judge how much infectious TB may be out there in any country at any given moment. As such it’s crucially important for strategic planning if you’re intending to defeat this infectious disease (particularly because it’s pulmonary TB that is assumed to be the source of most ongoing infections).

And then it’s from this surveyed prevalence (with the additional benefit of some more expert opinion about CDR) that the numbers of new ‘incident’ cases occurring each year get estimated and officially reported.

You will already have realised, of course, that there is therefore invariably a vast amount of ongoing uncertainty in both incidence and CDR, but with a national prevalence survey both global and national authorities are at least given something reasonably solid to work from.

The most recent National TB Survey in India...

So when was the most recent national prevalence survey conducted in India?

The most recent (and so far only) Indian nationwide prevalence survey was conducted by the Indian Council of Medical Research between 1955 and 1958. This survey provided, for the only time so far, a data set of reasonably accurate information on TB disease in the general population of the country at any moment of time.

Quite a lot has changed since then in the wider world of TB (and also in India) in the last 60 years, of course: India launched its National TB Program, for instance, in 1962; the disease was officially declared a Global Emergency in 1993 (and the same year a ‘Revised’ National TB Control Program was launched in India to make up for lost ground); later in the 90s the standard six month four-drug DOTS (‘directly observed treatment short course’) therapy was approved and implemented globally; and two years ago a special High Level Meeting was convened at the UN which belatedly committed all the world leaders to eradicating TB by 2030 – and in the same year Prime Minister Modhi announced that TB would be ended in India by 2025, five years sooner.

See-sawing data over the last eight years

Those findings from back in 1958 are very revealing. They suggested that the prevalence of TB in India was then about 400 per 100,000 population (with the population at the time making for around 1.5 million potentially infectious cases in India that year). Using the most recent published ratio between prevalence and incidence (from the 2016 WHO Global TB Report), this would possibly have amounted in 1958 to an incidence of about 1.1 million new cases that year.

For comparison, most recently this annual incidence has been estimated to be 2.64 million new cases in 2019 (strongly suggesting that a lot must have gone wrong with TB control in India in the last 60 years). Unfortunately, the WHO haven’t published prevalence estimates for any countries since 2016, but this would probably amount to around 3.5 million prevalent ones potentially infecting others in 2019 – or a prevalence rate of around 250/100,000.

So rather confusingly, over a period of sixty years the rates appear to have dropped by about 35% while the actual number of infections appear to have risen by 145%. If you’re confused by this, it’s simply because the national population has itself almost trebled in this same period (from 430 million to 1.37 billion).

Here’s a table that hopefully illustrates some of this.

This table identifies the1958 baseline, and then picks up the estimates published in each year’s Global Report from the 2013 one (reporting on 2012) through to 2020 (reporting on 2019). It should be especially noted that 2015 marked the start of the new era of the UN's ‘Sustainable Development Goals', which simultaneously launched a ‘New Era of Monitoring’ for the WHO and its member nations to enable particular milestone years for ending TB to be monitored, the first of which is for this current year, 2020 (which makes data for this year especially important)..

If we only look at the trends in CDR, it does look quite possible (given the 19% upward trend in case detection since 2015) that without the coronavirus the 2025 goal would have been achievable (but the current pandemic has sadly made it impossible now).

But you will also immediately notice how the CDR jumped in 2014, and then fell back with the estimated number of new cases themselves jumping the year later, the first year of the “WHO New Era of Monitoring” as part of its game plan to ‘end’ TB by 2030.

So what was happening that year? Well, trying to answer this question exposes serious concerns which remain unanswerable without reliable prevalence survey data which itself appears to have become a problem...

The 2016 Global TB Report (with the “larger than previously estimated” Indian epidemic)

The 2016 Global Report (the same one that recorded the new increased estimate of TB burden for India) put on record that the Indian TB epidemic was “larger than previously estimated”, explaining that this new assessment had been made on two counts.

One was because a provincial prevalence survey in a single Indian state had been completed three years earlier and this had exposed higher than expected rates of prevalent disease (its results only released in 2015). This survey had taken place in Gujerat, which was reckoned to be fairly typical, if not possibly better, than most of the rest of the country with regards to its prevalence of TB so these results were worrying.

It’s worth noting what the national prevalence for India might have been reported for 2015 if it had been directly extrapolated from this survey in Gujerat: it would have been running at 390/100,000 (or almost the same as what had been exposed in 1958) and so would have been much higher than the prevalence of 250/100,000 that previously been reported for 2014. So this immediately identified the possibility that literally millions of Indian TB cases might be being missed each year in India.

What was adding to these concerns was that for some reason this Gujerati prevalence study had been carried out in 2011 but had not had its results made public until the WHO used it to re-estimate the Indian TB burden in its global report of 2016. At the same time as this was finally published it was also cautiously reported in the Indian press that “a government official who did not wish to be named said that the health department had been sitting on the report for nearly three years”. It’s reasonable to wonder why he didn’t want to be named.

The second factor that had impacted on the WHO’s re-assessment was a paper that had also been published that same year in the Lancet. Submitted by a team from Imperial College London, it had carefully reviewed TB drug sales across the country and concluded (because of the massive sales of TB drugs) that a vast number of Indians with TB symptoms must have been avoiding notification in the national TB programme and resorting to unregulated private practice. This study even went so far as to suggested that the number of prevalent cases in India in 2015 might be as highs 3.8 million.

This left not much choice for the authorities. The WHO’s estimates for India (and, because of the disproportionate amount of TB in the country, also for the whole world) simply had to be hiked that year along with some sort of cautionary explanation as to why this had happened. These hikes were for both incidence and mortality but, quite bafflingly, at the same time the rolling estimates of prevalence were dropped completely from the Global Reports and have never been reinstated since.

The 2016 Report re-estimated that 2.84 million incident cases had occurred in India in 2015 - around a 30% increase on the year before. (In the absence of any prevalence data from this year onwards, we can do no more than apply the prevalence/incidence ratio from the previous year and so can suggest that a pretty terrifying 3.2 million infectious cases might have been out there in India in 2015). Because of the Lancet report, the WHO also added a careful caveat, identifying that a further national survey was in the pipeline and that this would help resolve the uncertainties; furthermore, reading between the lines, they seemed to be suggesting that it might well throw the new estimates further upwards.

It’s certainly possible that the Indian government may not have been thrilled by this assessment.

Here’s exactly what the WHO had to say on the matter in its 2016 Report. “Estimates of the burden of TB disease in India have been revised substantially upwards for the period 2000–2015, compared with those published in previous reports. This follows accumulating evidence from surveys and routinely collected TB notification data that previous estimates of cases and deaths were too low. As the country with the highest burden of TB disease in the world, these revisions have had a major impact on the global estimates. The estimates for India are still considered as interim, pending a national TB prevalence survey scheduled for 2017/2018.”

The '2017/18' National Prevalence Survey

It’s been Madukhar Pai in particular, the Director of the McGill International TB Center in Montreal, who’s been a lone voice expressing his concern about this since then, particularly focusing in the ICL Lancet paper. “Tuberculosis drug sales data” he recorded, “show enormous amounts of drugs prescribed in the private sector” adding that “prevalence surveys are, therefore, crucial to get the real burden.”

All was looking encouraging, though – with a national survey in the pipeline a proper idea of India’s true TB burden was at last going to soon emerge: India’s first TB prevalence survey since 1958 was scheduled to be begun in 2017 and to complete in 2018.

Not so surprisingly, we’ve been keeping a careful eye on this ever since.

The WHO’s Report of 2018, the following year, belied this 2017/18 schedule by revealing nothing beyond the fact that the survey hadn’t started in 2017, instead stating (without any explanation) that it was now scheduled to start in 2018. Estimates of TB burden in India will be updated once results from a national TB prevalence survey planned for 2018–2019 become available.

That same year, Dinesh Sharma, an award winning Indian journalist, reported in the Lancet that “at a summit in Delhi on March 13 [2018], Prime Minister Narendra Modi launched a campaign to end tuberculosis by 2025”.

We assumed from this that survey work must already be well advanced for the Prime Minister to have sufficient grasp on the burden of disease to allow him to make such an announcement. But the following year’s WHO report glossed over the matter again with no further India-related adjustments to its ‘interim’ estimates emerging anywhere, and with no reference to Mr Modhi’s announcement.

And now this last year’s Report (published two months ago) suggests that the survey had been rescheduled - now for 2019-2021 - (without referencing the fact that it would be finishing three years late and was now apparently destined to take three years to compete instead of two). It was reported as if nothing was amiss, and the study’s final belated launch in September 2019 was even formally announced with some fanfare in the Indian press.

In fact it was even reported without the faintest irony in the Lancet by the same journalist who had reported Mr Modhi’s 2018 announcement. The article was disingenuously entitled ‘India launches tuberculosis prevalence survey’ as if everything was normal.

Just like the WHO Report it included no reference to the three-year delay which was occurring in the critical first half of a self-imposed seven year programme to end TB in India. Similarly it also failed to observe the fact that any significant retrospective adjustments that might be made from its findings would essentially render conclusions drawn in 2020, the first way-marker year for the ‘EndTB’ strategy, meaningless. (The year 2020 is a milestone one for assessing TB targets for ending TB by 2030). The Lancet article simply reported that: “Now the Ministry of Health has launched a national prevalence survey to estimate prevalence of tuberculosis at national and subnational levels”.

So, in September 2019 India’s health minister Harsh Vardhan finally flagged off a state-of-the-art van – one of 25 that were intended to screen nearly 500,000 people in 625 districts across the country for TB – to kick of the survey. This would, he reckoned, take about six months to complete. If this had been the case then the data would (and should) have been well on the way to being analysed by the time the coronavirus hit India and the country went into lockdown. In the end it seems self-evident that this six month schedule is now just one more programme that has gone by the board because there’s no sign anywhere that the study was completed by March as should have happened. In fact there’s little sign that it ever really got off the ground by then – and now everything is clearly completely thrown into confusion by the coronavirus.

As the WHO itself explained two months in the Global Report ago: “As of August 2020, the survey was on hold due to the COVID-19 pandemic.” And, almost as an aside, it added that: “Updates to estimates of disease burden are expected in 2021 for India, following the completion of the country’s first-ever national TB prevalence survey.

So just how challenging is this task?

In this same Lancet article, Soumya Swaminathan (a Chief Scientist at the WHO) was quoted as saying that that: “Due to the size and complexity of the country … it is a challenge to conduct a rigorous, truly representative survey that will provide rates for the country as a whole”. We certainly cannot deny this, but then we’d add that there has been more than sixty years in which this could have been figured out.

Furthermore, he adds that “since the goal [of a prevalence survey] is to inform policy and strengthen the tuberculosis programme towards elimination, it is important to ensure that both the design and conduct of the study are of a high standard.” So is it reasonable to suggest that the WHO and the Indian Ministry of Health are not completely on the same page about this still, but meanwhile both are choosing their words too carefully for fear of upsetting each other?

Whether or not this is the case, a rolling death toll of millions of Indians is accumulating from a disease which the country’s Prime Minister plainly believes is entirely defeatable.

It’s certainly difficult to make out where either agency stands on the matter, and it’s a worry that no voices appear to be expressing the sort of concern that this deserves. After all, half a million are still reckoned to be dying of TB each year in India, but it may yet be revealed that this number is higher still. The fact is that this survey could (and should) have been completed before COVID-19 was ever heard of - and this failure will almost certainly have significant impact on health of the people of India in the coming years.


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