Estimation of State and district-specific disability adjusted life years (DALYs) due to tuberculosis for Kerala, India, 2017-2020

Material & Methods

The study was conducted at the department of Community Medicine, Government Medical College, Kollam, Kerala, after obtaining the ethical approval from the Institutional Ethics Commitee.

Results

There was an increase in the relative DALYs in Kerala from 2017 to 2019. The DALYs due to TB in Kerala was lowest at 1124 in 2020 and highest at 1482 in 2019 during the period 2017 to 2020 (Table I). The contribution of years lived due to the disability was 96-98 percent of the total DALYs (Table I and Fig. 1).

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Fig. 1.

Years of life lived with disability (YLD), Years of life (YLL) lost due to Tuberculosis in Kerala from 2017 to 2020. DALYs, disability-adjusted life years.

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Among the districts, Thrissur, Kollam, Kasaragod, and Idukki showed a steady decline in DALYs from 2017 to 2019. Idukki had the least DALYs since 2018 consistently. Thiruvananthapuram, Kozhikode, Kannur, and Kottayam showed an increase in DALYs from 2017 to 2019. Kottayam, a district that had the least DALYs in 2017 has become the district with the highest DALYs in 2020 (Table II).

The districts with the highest reported cases were not the same as those with the highest DALYs. During 2017, the highest notification of incident TB was seen in Thrissur, followed by Ernakulam and Kollam. However, Wayanad and Ernakulam had the highest burden in terms of relative DALYs after Thrissur. Kollam also recorded the highest TB death rate in 2017 but it had only the fourth-highest DALYs (Fig. 2 and Supplementary Tables I–IV).

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Fig. 2.

Burden of TB in different districts of Kerala over the years; (A) 2017, (B) 2018, (C) 2019 and (D) 2020. I/incidence, incident TB notification; M/mortality, reported TB mortality rate; RD, relative DALYs.

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In 2018, Wayanad in terms of incident TB notification ranked only seven, but it ranked first in mortality. The median age of onset was 35 yr, which was much lower than other districts. The median age of mortality was 54 yr, which was also lower than other districts. Hence in terms of DALYs ranking, Wayanad has the highest burden compared to other districts. A similar phenomenon was seen in 2019 and 2020 also.

To make a conclusion on the burden of TB in districts, the DALYs ranks for the years 2017 to 2020 were added and the effective DALYs rank was calculated. The district with the lowest sum would be the one with the highest burden considering all these years. Ernakulam and Thrissur districts had the highest burden and ranked first; Idukki had the least burden (Table III). The relative DALY/lakh population in the district across these years is shown in a choropleth map (Supplementary Figure).

Discussion

DALYs estimates for TB have increased from 2017 to 2019. This could be due to an increase in case finding and closing the gap in the surveillance system through active efforts at TB detection in the State in the context of TB elimination, which started in 2017. In 2020 DALYs is seen to be lower than that in other years. This could be due to the influence of the COVID pandemic in TB-related activities. COVID has adversely affected our march towards TB elimination. There is a reported five per cent annual shortfall in case notifications in 2020 compared with 2019¹. But it is also noted that the TB case fatality has increased slightly from 2017 to 2019 in Kerala. Other studies show that mortality and incidence of TB decreased across all age groups for both males and females over the period 1990–2019⁴. It could be because of the efforts in capturing all TB cases including deaths and also because TB has mostly affected the elderly community and the risk of mortality is higher in this age group.

The total DALYs in India in 2016 was 1316 million and the contribution of TB was 3.2 per cent, which is 3166/100,000. It declined compared to 1990 when the total DALY was 8640 million and the contribution of TB was five per cent (relative DALYs 4948/100,000)⁸. The maximum relative DALYs due to TB in Kerala from 2017 to 2020 is 1482/100,000. This is only half the burden compared to Indian figures (1482/3166). According to estimates from the GBD studies, TB contributed to 6.5 per cent of the total DALYs due to communicable diseases in all ages, and this increased to 17 per cent of DALYs in the population aged 65 yr or older in 2017¹⁶.

In the GBD studies, TB-related burden in Korea from 2014 to 2017 was estimated to be 111, 107, 104, and 105 DALYs/100,000 populations, respectively¹⁷. Compared to this the burden due to TB in Kerala is 10 times higher. In Korea, the DALYs clearly showed a declining trend¹⁷. In our study, the DALY from 2017 to 2019 showed an increasing trend. There is clear evidence that there has been an increasing notification in India since 2017-2018, which indicates the efforts put in the TB programme⁸. DALYs sin our study is calculated based on officially reported cases. We acknowledge this as a major limitation of the study. There could be cases that are undiagnosed or not reported to the programme. However, such proportions might be very minimal in Kerala^18,19.

In Korea from 2014 to 2017, the DALYs calculated for drug-sensitive TB was 56, 49, 46, and 40, respectively, and DALYs per 100,000 people with MDR-TB were three, two, two and two, respectively²⁰. We have not calculated DALY separately for drug-sensitive and drug-resistant TB. Researchers have also attempted to model DALY for future years, which was not done in this study¹⁷. TB-related DALYs are greatly underestimated by overlooking post-TB disability²¹. The disability weights used in this study also have not incorporated post-TB sequel. However, as per author’s knowledge this is the first attempt to generate the State and district-specific TB DALYs.

There is a need for capacity building for DALYs estimation so that programme officials have the information and can interpret them. The estimation of DALYs due to TB provides an alternative and more accurate approach for programme implementers and policymakers to understand TB burden, compare across administrative units, and monitor its trends while reviewing programme performance and progress towards targets. The global monitoring indicators for TB can also be carved better uniformly in this direction. More studies using DALYs are required to find the burden of drug-sensitive and drug-resistant TB, incorporating the weights for post-TB sequel and modelling for future predictions.

We have not attempted to classify the burden by type of TB, type of disabilities and age-specific DALYs, which are areas for future research. Limitations of DALYs estimates in general, like the subjectivity of disability weights, more value given to life at younger ages, lack of consideration of the severity of disease, and reliance of estimates on the quality of data source, also apply to this study^22,23.

Overall, DALYs estimates calculated based on official surveillance system data for Kerala show an increasing trend before 2020, which could be due to the increased efforts to detect TB as part of the elimination drive. In 2020, the burden is found to be lower and it could be because of COVID. However, the burden due to TB in the state is much lesser compared to India. The districts that reported higher rates of cases were not the same as those found to have higher DALYs. The use of DALYs gives a more comprehensive assessment of the burden of TB, which is different from the assessment using incidence and mortality alone. Prioritization of districts for resource allocation may be done more accurately by using DALYs. It may also be considered in the Government of India’s sub-national certification of TB-free status for districts and states.