TB in South-East Asia

Epidemiology of TB in the Region

The South-East Asia Region, with an estimated 4.88 million prevalent cases and an annual incidence of 3.17 million TB cases, carries one-third of the global burden of TB (Figure 1). Five of the 11 Member countries in the Region are among the 22 high-burden countries, with India accounting for over 20% of the world’s cases. Most cases occur in the age group of 15-54 years, with males being disproportionately affected. The male/female ratio among newly detected cases is 2:1. Though deaths due to TB have declined after introduction of DOTS.

Source: Global Tuberculosis Control Surveillance, Planning, Financing, WHO, Geneva, 2009

TB incidence, prevalence and mortality

The control of tuberculosis in the Region is affected by variations in the quality and coverage of various TB control interventions, population demographics, urbanization, changes in socio-economic standards, HIV and, more recently, emerging drug resistance. Table 1 shows the estimated TB incidence, prevalence and mortality rates for countries in the Region.

Table 1: Estimates of TB disease incidence, prevalence and mortality in the South-East Asia Region, 2008

* UN Population Division, World Population Reports, 2007, New York (Rev.)

Figure 2 shows the estimated TB prevalence rates in the 11 Member countries of the Region comparing the rates between 1990, 2004 and 2007. These are indicative of a decrease in all countries of the Region.

Source: Global Tuberculosis Control, WHO Reports 2001-2008

Figure 3 shows the estimated TB mortality rates for all forms of tuberculosis per 100 000 population, comparing the rates between 1990, 2004 and 2007. With respect to 1990, a significant decrease is observed in 2007 in all countries of the Region.

Source: Global Tuberculosis Control, WHO Reports 2001-2008

Figure 4 shows the overall trends in the estimated TB prevalence, incidence and mortality rates per 100 000 population in the Region as a whole, between 1990 and 2007. The estimated prevalence and mortality rates decreased slowly between 2004 and 2007.

Source: Global Tuberculosis Control: WHO Reports, 2001-2008

TB infection

Annual Risk of TB Infection (ARTI) studies undertaken in countries have revealed widely disparate results. Studies in four zones in India carried out during 2000-2003 showed ARTI rates ranging from 1.0 % in the south zone to 1.9% in the north zone; repeat ARTI surveys are being undertaken, but the results are not yet available. In Indonesia, an ARTI study carried out in 2006 in West Sumatra yielded an incidence rate of 1.3%. A limited ARTI survey undertaken in 2008 in DPR Korea is indicative that the incidence rates for the country as estimated by WHO may need to be revised upwards by a factor of two. Nepal undertook an ARTI survey in three ecological zones and in the Kathmandu valley during 2006-2007, revealing a rate of 0.86%, substantially lower than the previous rate of 2.1%. Similar surveys are planned in Bhutan and Sri Lanka in 2009.

TB disease incidence, prevalence and mortality

While these surveys are indeed contributing to more accurate estimations of the burden of disease in countries, there are still uncertainties about the current estimates for TB disease incidence, prevalence and mortality rates in individual countries in the Region. The use of routine notification data as a measure of disease incidence is certainly the way to go in the future. This however requires strengthening all aspects of the TB surveillance system, focusing on quality of data entry, compilation and reporting, and giving attention to precise analysis and interpretation of the data. As part of this effort, the WHO Regional Office for South-East Asia (SEARO) organized a series of trainings on managing information for action (MIFA) in four Member countries during 2007-2008. Meanwhile there is clearly a need to continue to support well-designed population-based surveys in the Region, particularly in the higher TB burden countries, until such time as routine case notifications can begin to be used to correctly reflect actual trends.

Impact of HIV on TB in the Region

The expanding HIV epidemic in the Region is a growing concern. Of the 31.6 million people estimated to be living with HIV in the world at the end of 2007, more than 3.6 million are estimated to be in the South-East Asia Region. India alone is estimated to have 2.4 million people living with HIV (Figure 5).

Source: Report on the Global AIDS Epidemic: UNAIDS, 2008

Three countries in the Region (Thailand, Myanmar and a number of districts in nine states in India) have rates of HIV > 1% in the general population and the highest HIV/TB co-infection rates in the Region. Four countries have concentrated epidemics: Bangladesh, Nepal, Indonesia and some states of India. While Myanmar and Thailand have a more homogenous and high HIV prevalence, only some states in India and three provinces in Indonesia report high HIV rates.

HIV does not appear to have fundamentally altered the epidemiology of TB in the Region to the extent observed in sub-Saharan Africa. Available data suggest that the incidence of TB has been minimally affected by the HIV epidemic. The impact on TB mortality however, has been much more substantial. In India, Myanmar and Thailand, high TB case-fatality rates have been reported in areas with high HIV rates in the general population.

Drug-resistant TB

Seven countries have reported data on drug resistance since 2002, namely, Bangladesh, India, Indonesia, Myanmar, Nepal, Sri Lanka, and Thailand. India reported data from three districts and one state, while Indonesia reported data from one district only. Orissa in India, Sri Lanka, and Thailand reported less than 2.0% MDR-TB among new cases. Districts surveyed in the states of Kerala, West Bengal and Gujarat in India as well as Mimika district of Papua province in Indonesia, and Nepal reported between 2.0-3.0% MDR-TB among new cases. Myanmar reported a higher level of 3.9% (2.6%-5.7%) MDR among new cases. While a few tertiary-care facilities have reported levels of multi-drug resistance as high as 60% among previously treated cases, these are not representative of the situation in the community.

Resistance to first-line anti-TB drugs is equally a concern for national TB control programmes in countries of the Region. The population weighted mean of MDR-TB based on all the countries that have reported in the South-East Asian Region is 2.8% (1.9%-3.6%) among new cases and 18.8% (13.3%-24.3%) among previously treated cases. However, given the large numbers of TB cases in the Region, these figures translate into nearly 150,000 cases in the Region as a whole, with over 80% of these cases residing in Bangladesh, India, Indonesia, Myanmar and Thailand. While Myanmar and Thailand report relatively lower rates of MDR-TB among new cases, the two countries report 15.5% and 35.5 % MDR-TB rates respectively, among previously treated cases, which is a serous concern.

Extensively drug resistant tuberculosis (XDR-TB), has been isolated in samples from India, Indonesia, Bangladesh, and Thailand. Given the widespread availability and use of second-line drugs, and as laboratory capacity to conduct second-line drugs susceptibility testing increases, additional occurrences of XDR-TB are likely to be identified.

The other concern is that unless well managed MDR-TB programmes are rapidly established under national programmes, MDR-TB cases will continue to be treated by the private sector through not necessarily well supervised or well designed second-line regimens, or through over-the-counter purchase of these drugs, given their widespread and easy availability, risking further increase in drug resistance.