The TB burden

Around nine million people contracted tuberculosis (TB) last year - nearly half a million more than were reported in 2012 - of which 1.5 million didn't survive, according to a World Health Organization (WHO) report released on Wednesday, October 22.

With more complete data coming out of South Asian countries like Pakistan, the international health body found that TB was prevalent in the Asian continent. While India accounted for 24 percent, China registered 11 percent of global TB cases, the WHO noted.

In a DW interview, Philippe Glaziou, senior epidemiologist at the WHO's Global TB Programme in Geneva, Switzerland, says that although progress has been made in a number of Asian countries since 2000, the burden remains comparatively high in India and Pakistan.

DW: The latest WHO report states that the number of people who have contracted the disease is on the rise. Does the same apply to TB-related deaths?

Philippe Glaziou: Overall, the number of TB deaths (excluding HIV) in Asia (WHO Western Pacific Region and South East Asia Region combined) is actually not increasing but decreasing, at an average rate of 5.3 percent a year over 2005 – 2013, which makes up 831,000 estimated deaths in 2005, and 543,000 in 2013. Including HIV-associated TB deaths, the average decline was 5.5 percent a year - 930,000 in total in 2005, and 600,000 in 2013.

Why was the issue underestimated?

The burden of TB is best measured through state-of-the-art surveillance systems in countries with universal access to healthcare and very high coverage of TB case notifications. In other countries, TB prevalence surveys are a reliable, albeit costly way of measuring the burden of TB in the general population.

There has been an unprecedented rise in the number of prevalence surveys in the past few years. In particular, a survey in Nigeria allowed generating more accurate estimates of TB burden compared with previously uninformative estimates.

A nearly complete survey in Indonesia, with final results expected towards the end of this year, will likely have the same effect. It is not always the case that surveys indicate a higher burden than previously thought. In some other countries, such as Rwanda and Gambia, the survey actually found a lower burden than previously estimated and in many others, there was no significant difference with the previous estimate.

India, Pakistan and China have high case numbers, as your report shows. What makes these countries more prone to tuberculosis than others?

China has high numbers due to the sheer size of its population, but TB burden expressed per capita is now much lower in China than in India and Pakistan. Some major determinants of (high) TB burden are well known: poverty, overcrowding, high prevalence of tobacco smoking or diabetes, and poor TB control practices in the past, among others. HIV is a major determinant of TB in general, but the epidemics of HIV in the three countries are at low levels and have not affected national TB epidemics in very significant ways.

Declines in TB burden occur faster in countries with universal access to healthcare and high coverage of quality services, including laboratories. Progress has been made in all three countries since 2000, but the burden remains comparatively high in India and Pakistan.

Why can't the disease be controlled in these countries?

The reasons why the TB rates do not fall faster are multiple. They include the lack of universal access to medical care. In the absence of health insurance and social protection, the poorest do not access health services when they are sick. They need to borrow money and may not be able to afford a day off work.

This contributes to undiagnosed TB and sustained transmission in the community. In countries with a strong but insufficiently regulated private sector such as India and Pakistan, the quality of services and the quality of care may not reach high enough standards, leading to poor treatment outcomes in diagnosed TB cases, further contributing to sustained transmission.

Transmission also occurs in hospitals and clinics in the absence of effective infection control. Poor medical care leads to higher levels of drug resistance, in turn increasing transmission.

With currently available tools, the fastest decline in TB incidence observed at national level over a period of about one decade did not exceed 10 percent. The decline is slow because a very large number of people, about a third of the world population, are infected with the TB bacilli, but do not have the TB disease, and every year, a small proportion of those infected become sick with TB. To reach faster declines in TB incidence, a vaccine more effective than BCG to prevent the development of the disease is necessary.

Philippe Glaziou is a senior epidemiologist at the Global TB Programme of WHO. He leads the work on estimating the burden of TB and its time trends in every country.