How can the Lancet report on mortality rates justify itself as the 'most comprehensive study' of TB, malaria and HIV?

Dr Theo Vos: The report is part of the Global Burden of Disease Study 2013 and looks at the incidents and mortality rates for the three diseases between 1990-2013. It's notable for its rigour, and for looking closely at the mortality rates and risk factor outcomes of individual countries over time. We have drawn together the largest collection of information and made comprehensive use of different types of data.

Do you think it will change how any of these diseases are measured?

Yes. For example, we made a big change in how to approach the estimates in HIV in countries that have infections concentrated in particular risk groups such as men having sex with men, IV drug users, and commercial sex workers. The typical approach of those such as UNAids was to try to estimate how many people were at risk within these groups. This however relies very heavily on things that are difficult to know, particularly in certain countries, such as patterns of sexual activity, how many people use IV drugs, and if so, whether they do it safely.

The alternative approach we took was to measure vital records of death. In many countries where you have concentrated epidemics such as in Asia and Latin America, increasingly you have more reliable data on cause of death.

Are there limits to what the report can tell us?

While it is more comprehensive than previous research, this doesn't mean that gaps won't remain. Often diseases such as HIV are hidden in the cause of death information; many doctors will say the patient died of something else to avoid the stigma associated with being infected. We tried to tackle this by using long-time series analysis on the cause of death information and comparing this with existing evidence. This method has given us fairly accurate estimates of the true level of deaths in these countries.

What were the surprise findings of the study?

The big headline is that there are very encouraging signs across all three diseases and also specific surprise findings. We realised that the HIV estimates we were working with were wrong – the epidemic is actually smaller than we thought, by roughly 25%. We have realised that previous efforts relied heavily on very uncertain assertions about the proportion of people that make up a risk category and the types of behaviour that leads to risk of infection. We also realised that we underestimated the duration of time between infection and death in the absence of treatment for HIV.

When it comes ot malaria, the study revealed it is killing more people worldwide than previously thought. However, malaria is a tough disease to measure. Most of the deaths occur in Africa where we don't have strong routine recording of causes of death, and even in places where you do, malaria can be hard for physicians to diagnose. In countries where malaria deaths are highest – Nigeria, Mozampbique, DRC, and India – you are often relying on verbal autopsy (where we ask the relatives to describe the circumstances of death).

What can be learned from the success so far in tackling these diseases?

The success is primarily explained by the unprecedented investment in this area under the millennium development goals. This has resulted in specific interventions in each of the three diseases. In HIV it is mostly investment in antiretroviral treatment which has proved to be much more successful than behavioural interventions that are hard to implement. For malaria, impregnated bed nets were very important but my suspicion is that maybe the scaling up of treatment appropriate to a country's level of resistance is perhaps been more effective. For TB it has been serious ramping up of coverage but also improving the quality of treatment: we're not really doing a whole lot more but doing it much more rigorously.

What impact do you hope the report will have?

All the successes detailed in the report rely on sustained effort. Looking forward to the post-2015 agenda, the danger is that policymakers could assume they can water down efforts in areas where we are seeing improvement.

However, we need to do more of the same but we also need new solutions: better diagnosistics for malaria, the vaccines for malaria or HIV that has been elusive for so many years, and we seriously need new drugs for TB. This is a critical area – we haven't seen a new drug on the scene for 30-40 years and we are seeing growing resistance.

So the key impact we want the report to have is to communicate to policymakers that although we're making a lot of success, that doesn't mean you can draw your interest away. If we do, these diseases will come back with a vengeance.

Explore the data visualisation of the report here.

Dr Theo Vos is one of the authors of the report and professor of global health at the Institute for Health Metrics and Evaluation in Seattle. Follow @uwghrc on Twitter.

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