Exploring the global burden of disease

In the 1990s, the World Bank turned its attention to identifying and organizing priorities for investing in the health of the developing world. Almost immediately they were met with the difficulties of gathering real data on the diseases and risk factors having an impact in developing nations. The World Bank realized then—and this work was taken up by the World Health Organization (WHO)—that an advanced methodology for measuring what we now refer to as the global burden of disease had to be developed. Before strategies for moving forward could be created, we had to define where we were.

From this realization grew a new approach to assessing the impact of disease, the short and long-term effects of risk factors, and the overall impact on the world’s communities. The ongoing Global Burden of Disease (GBD) project, led by Christopher Murray of Harvard University and Alan Lopez of WHO, seeks to capture a reality of the world’s health based on sophisticated, unbiased measurements. It’s a massive undertaking involving the work of over 100 people focused on specific regions and disease areas.

Influenced by many factors, the global burden of illness is changing. People in general are living longer—and therefore there is increased suffering from chronic diseases. Populations of once dominantly rural nations are flocking to urban areas, drawn by the economic opportunities created by modernization and technology—leading to reduced physical activity, more traffic accidents, and a dramatic rise in cases of conditions like obesity, diabetes, hypertension, and coronary artery disease. In this issue of HMI World, two leaders working in very different arenas to address the global burden of disease offer their unique perspectives. Murray, the Richard B. Saltonstall Professor of Public Policy at the Harvard School of Public Health, discusses how to measure the world’s illness. Robert K. Crone, MD, president and CEO of Harvard Medical International, examines how health care systems around the world are responding to the evolving needs of patients and communities. Drawing significantly from information collected in the WHO’s 2002 publication of the World Health Report, we also take a look at today’s burden of illness, and where trends indicate we are headed.

Time moves at two speeds in the global health care community. International epidemiologists must track the trends that present a picture of the burden of disease for decades to come, while policymakers work to align strategies and resources with those trends. At the same time, frontline care providers are challenged to respond to the health care issues facing them in their communities today. Their immediate concern is not with theoretical projections, but with actual waiting rooms, emergency rooms, and clinics.

For decades, health officials employed crude indicators to measure community health, such as birth rate, death rate, and infant/maternal mortality. But because of the work of WHO, the impacts of disability and premature death—in loss of productivity and life years—are now figured into the measure of the burden of disease. For the GBD project, an internationally standardized metric has been developed, called the Disability-Adjusted Life Year (DALY). The DALY expresses years of life lost to premature death and years lived with a disability of specified severity and duration (one DALY equals one lost year of healthy life).

“It is no longer possible in my setting to think about health only in terms of mortality rates,” said Murray. “Blindness is a good example of a health problem that, while not causing death, can dramatically reduce one’s quality of life or ability to function within society. Once the issues surrounding disability are brought onto the policy agenda, they are difficult to avoid. It’s important to remember that most of what the health care community does is deal with illness, not just death.”

But collecting accurate data from countries remains a challenge, either due to human error or flaws within the system. “There are miscalculations pertaining to cause of death, and situations where advocacy groups connected to a certain disease skew the data because of their bias,” Murray said. “The job of the global burden project is to determine what the facts are.”

The shifting burden of disease
The work of Murray and his colleagues suggests that the global burden of disease will undergo a process of dramatic change during these next two decades. Although epidemiological studies strive to assess the health of the entire world’s population, it is impossible to ignore the fact that four-fifths of the world’s people live in the developing regions. In these areas, noncommunicable diseases such as depression and heart disease are replacing problems such as infectious diseases and malnutrition as the leading causes of disability and premature death. While these problems remain huge sources of suffering in the developing world, it is clear that due to a number of factors, the prevalence of “adult” diseases that plague people for many years is increasing. Today, noncommunicable diseases account for less than half of the deaths in developing regions, but the GBD study estimates that by 2020, that percentage could rise to 70 percent.

Several factors are at work in this epidemiological transition, which has outpaced public health policy. Perhaps most importantly, populations are aging. Improvements in health care have led to increased child survival, and diminished maternal morbidity and mortality. Higher literacy rates and better education have led to increased health awareness and a reduction in the birth rate. As a population’s birth rate falls, the number of adults relative to children increases, and the population’s most common health problems become those of adults. With life spans for both men and women on the rise globally, more and more people reach the at-risk ages for chronic diseases.

Another key factor is the demographic shift that has the populations of developing countries moving to cities. In China, for example, more than half of the country’s 1.4 billion people live in urban areas. This urbanization, coupled with the advancement of technology and therefore more “sedentary” jobs, is leading to sharp reductions in physical activity. Today, fewer people are employed in manual labor jobs, more people are tethered to desks and computers, and more tasks are automated; more people are driving, rather than walking; conveniences are lightening the domestic labor load; and finally, in those hours when one might be on a bicycle or a jogging path, more people sitting on couches watching television, or playing computer games. All of these changes open the door to a multitude of risk factors related to noncommunicable diseases.

Disease outlook for 2020
The GBD study suggests that the burdens of mental illness, such as depression, alcohol dependence, and schizophrenia, have been seriously underestimated by epidemiological approaches that measure only deaths. Psychiatric conditions, while resulting in a little more than one percent of total deaths today, account for 10.5 percent of the global disease burden. By 2020, this could rise to 15 percent, a larger projected increase than that for cardiovascular diseases. Unipolar major depression is projected to rank second in DALYs by 2020.

Ischemic heart disease, road traffic accidents (RTAs), and chronic lung disease are all expected to comprise a more significant percentage of the burden of disease. Lower respiratory infections, diarrheal diseases, and perinatal diseases—the top three contributors to the burden in 1990—will see dramatic reductions in terms of their share of the global burden of disease (see table).

Finally, perhaps the most disturbing projection to emerge from this study: by 2020, tobacco is expected to kill or disable more people than any single disease, even surpassing HIV/AIDS. This is a health crisis that many nations have yet to address (see sidebar).

Health, economics, and government: new thinking and new roles
The WHO Commission on Macroeconomics and Health has been among the organizations that have explored the links between higher levels of health and economic prosperity—or in the case of the developing world, the all-too-common opposite. Southeast Asia may be viewed as one example of a region where this correlation was demonstrated. A revolution in health care between 1950 and 1965 was a significant factor in an economic boom in the region.

Crone, who regularly speaks on the burden of disease to audiences around the world, says measuring disability is important because it underscores the close correlation between the health of a community and its economic progress. “Conventional wisdom in years past has been that countries should not invest in health until their economy is stable. But the new thinking that is taking hold around the world is that an investment in health is an investment in a more productive population,” he said. “Healthier people live longer and devote more resources to developing skills and education. This feeds back into the health care system for lasting benefits.” For the poorest of people, even if a bout of disease does not result in death, it can destroy a family and its livelihood. The same is true in wealthier nations, but in much of the developing world, there is little to protect people living on the cusp of absolute poverty.

The volatile political climate in much of the world suggests that wealthier nations must take a vested interest in assisting the developing world in overcoming their problems. “Disparities in health and economics are a national security risk for even the wealthiest of nations,” said Crone. “This realization may focus some badly needed attention and resources from the international community.”

The role of government in health care is changing in many countries. In countries where the government is both the provider and payer of the health care system, there is very little to drive improvements in the health care delivery system. Systems can be underfunded and inefficient—or simply fail to provide high-quality care—but because the political and health care systems are linked, patients in countries like the UK have little recourse but to voice their objections at the ballot box.

In China and the United Arab Emirates, the governments, instead of continuing to provide all of the care, are fostering the development of alternatives in the private sector. The governments are transitioning to a stewardship role wherein they act as a regulator and arbitrator between the three points on the health care triangle: providers, patients, and payers. Crone said, “This still allows for a safety net for those who cannot afford care, and also frees the government to regulate hospital standards and serve as a steward for patient safety.”

The HIV/AIDS epidemic: long-term impacts on health care systems
The GBD study suggests that public health policy, with its traditional emphasis on infectious disease, has not kept pace with health trends. This slow—or perhaps, reluctant—shift of resources to combating noncommunicable diseases is due in part to the devastation of the HIV/AIDS epidemic. In places like Africa, it simply cannot be ignored—the numbers for noncommunicable diseases, though rising, still pale in comparison to the statistics regarding HIV/AIDS. In fact, many studies examining the differences between problems affecting the poor and the wealthy suggest that the global poor would benefit more from faster progress against communicable diseases; progress against noncommunicable diseases, despite their growing prominence, would more benefit the wealthier—and smaller—population.

“ The HIV pandemic stands out as a remarkable event in our history. The impact is likely to be larger than that of the Black Death,” said Murray. “The 1918 influenza epidemic, previously the largest global disease outbreak, was over in two years.” That epidemic killed somewhere between 20 and 40 million people worldwide; AIDS has already resulted in over 20 million deaths, and today more than 40 million people are living with HIV/AIDS.

In sub-Saharan Africa, as much as a quarter of the population is infected, causing a severe population imbalance between dependent and productive peoples. Here HIV is threatening to reverse some of the gains made in the last fifty years. Much international attention has been focused on this, and the money and antiretroviral drugs are being made available. But the health care delivery system dealing with it is stretched to the limit and beyond—money has proved to be just one resource that is necessary to carry on the fight. Crone said, “Although deaths from infectious diseases will decline worldwide, the combination of infectious disease, particularly HIV, with the superimposition of the modern burden of disease will enhance the devastation in sub-Saharan Africa.”

Finding optimism in what is possible
Many who are focused on the global health care community, and specifically the developing world, believe that with modern technology and scientific advancement—and the commitment of resources from the world’s wealthier nations—the great health care dilemmas can be resolved. Murray says that despite success of public health and clinical care initiatives, “Going forward, we face the question of figuring out which people have been left out of that. Africa, particularly the sub-Saharan region, still has far to go.”

Perhaps surprisingly, he finds much to be optimistic about in his work. “In the period between around 1900 and 1980, we had the most dramatic transformation of human biology ever,” he said. “This is a story of steady progress everywhere in the world, albeit with a few bumps along the way. It was an unprecedented period in terms of the lengthening of life and improving the quality of life.”