Targeting Transmission of Tuberculosis

by Line Bager (@lbager87)

On the 11th of November 2014, the London School of Hygiene and Tropical Medicine (LSHTM) and University College London hosted a small conference for the research community to discuss the ways in which Mycobacterium tuberculosis (TB) is transmitted. In a lively talk between Helen Ayles, LSHTM, and David Dowdy, John Hopkins Bloomberg School of Public Health, the prospects of ambitious Active Case Finding (ACF) were debated. Attending this conference as a graduate, with a non-medical and non-scientific background, it was interesting to see what the researchers focused on. The line was drawn rather sharply, perhaps partly for entertainment value, between ACF as a key strategy, actively searching for at-risk individuals, and the opposing view that argued ACF will not have an effect on the rate of transmission overall.

Mycobacterium tuberculosis
Mycobacterium tuberculosis

At the heart of the issue lies TB’s treacherous nature – a person can be infectious for several months before showing symptoms and to make matters worse, symptoms can be confused with many other diseases. During that time, hundreds of people could become infected through the spread of bacteria in the expired aerosols of infected persons. But is ACF really plausible? In a population of millions, how do you find those with TB if you are not testing every single one? From a cost perspective, targeting an entire population simply isn’t feasible. And even if the funds were there, how would you reach the most remote areas? As an economist myself, the pervasive paradigm of cost-benefit analysis is very difficult to escape. As was pointed out at the conference; “TB is not the only affliction of humankind”. The death toll from TB does not come anywhere close to that of heart disease. How much do we actually gain from increasing the spending for ACF? As brutal as it may sound, the funds could probably be spent more efficiently elsewhere.

But let me outline a scenario. Take an individual living in a poor and semi-urban setting, perhaps in Southeast Asia (SEA) or sub-Saharan Africa (SSA). This individual has an insecure income, no formal training, lives in crowded housing and on top of all of this, has active TB. Some might argue that this perpetuates the stereotypical view of SSA or SEA but it is also the reality for many millions of people living there, constrained by their environment. The reality is that many millions of people are facing multiple vulnerabilities and not just with regards to their health. Typically they have no or limited access to health care. TB is not uncommon in many low and middle-income countries, where 96% of infections occur. So it is clear that TB does not target individuals uniformly. In fact, the countries with the highest proportion of TB are Cambodia and South Africa. So even though TB should not be the only disease we focus on, since it hits the poorest and most vulnerable communities, not doing anything is definitely not an option. This little scenario outlines that it is not just the total number of deaths or the level of morbidity that count, but where it happens: whether there is existing infrastructure to reach and treat infected individuals should also be taken into account.

Probable tuberculosis
A case of probable tuberculosis.

Besides, when Helen Ayles advocated for ACF, she wasn’t talking about testing every single individual in every low income country. Maybe she had a fair point when she argued that the so-called ‘TB community’, could be more ambitious and could have a better testing system. Targeting at-risk communities and individuals is a first step. But perhaps it is not a case of identifying people as soon as they are infected but rather before they are so weak that the disease has deprived them of their livelihood and life – which is often the case. It is not a question of chasing every single case of TB as if resources were unlimited, but rather to be more ambitious and exploit possible coordination gains with the screening and treatment of other diseases such as HIV.

A Johannesburg slum: Individuals living in such conditions are disproportionately affected by TB.
A Johannesburg slum: Individuals living in such conditions are disproportionately affected by TB.

In my opinion the question of improving ACF is not getting to the heart of the problem. Asking to what extent ACF can be useful is indeed valid, but it can only have a limited application. It is interesting to note that the decline in TB prevalence happened before the widespread use of antibiotics. What proved the most effective for TB prevention in Europe in the 19th and 20th century were hygiene improvements, nutrition and better housing. Hence, the emphasis on medical advances is sometimes misplaced when it focuses on specific programmes or has a narrow aim. What it boils down to is whether we are targeting the proximate or the ultimate causes of TB. Ultimately, development has historically proven to be the most effective prevention of TB. Hence, structural change in low-income countries is key to generating the resources, underpinning improvements in education, health-care, etc. Therefore, we should never rely on Active Case Finding on its own: it should be secondary to active case prevention – fundamentally improved living conditions.

For videos on the transmission and treatment of TB, click here.

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