Online newsletter Volume 2, Number 3,  Winter 2004-2005

Risk Patterns Old and New

Public Health's new world challenge
 

Increasingly, travel in low- and middle-income countries is becoming more motorized—in three-wheeled mini-cabs, scooters, modified pickups, and other small, cheap vehicles as well as transit buses and jitneys—a reflection of rising prosperity and resulting in much greater mobility. But these gains are not without a price.

Of the approximately 1.2 million deaths that occur each year due to road crashes, 85 percent occur in low- or middle-income countries, and low- and middle-income countries account for 90 percent of the annual disability burden caused by traffic crash injury (See a related story in this issue, “Measuring the Burden”).

Furthermore, this rising rate of traffic fatalities in low- and middle-income countries is but the most prominent instance of a more general shift that has occurred over the last decade. Whereas disease, and predominately infectious disease, has traditionally presented the biggest global health threat, unintentional injury and violence have begun to pose still greater threats, particularly among young people between the ages of 10-24, a group whose high rates of migration into cities across the globe has exposed it to, among other hazards, the dangers of the road. Furthermore, according to a study conducted by the European Union Injury Prevention Program, road traffic injuries, along with self-inflicted injuries, are the most common type of injury death worldwide. When studying unintentional injury worldwide, it is crucial to examine the factors contributing to the rise in traffic deaths and to explore the best strategies for reversing this trend.
 

Traffic deaths: a new challenge for the public health community 

Despite the shift described above, injury is over-shadowed by disease in the emphasis that it receives from the public health community. In the U.S., funding for injury prevention and research is significantly below that for chronic disease prevention. Injury prevention received $154 million from the Centers for Disease Control (CDC) in the year 2004 compared to $853 million allocated to chronic disease prevention, despite the fact that injury-attributable medical expenditures are high—$117 billion in 2000 as compared to $60 billion for cancer in 2002, according to an article that appeared in the Trauma Foundation’s newsletter in July 2004. As the author of the article observes, because trauma injury does not have its own institute in the U.S., and “because government funded entities (including the National Institutes of Health, the National Science Foundation, and the CDC) do not specifically identify injury-related issues … it is difficult to determine the current level of funding for traumatic injury-related death and injury.”

The increased prominence of injury is still relatively recent, and there is little reliable data, because there are few mechanisms in place in low-income countries by which to record traffic crash injuries and fatalities. Nearly two-thirds of the world’s countries, most of them the world’s poorest, do not collect any statistics on traffic crashes. As a result, traffic fatalities and injuries, even when treated with the same urgency afforded communicable diseases, have not been easy to put in context in terms of the threat they pose and how they might be reduced by different interventions.
 

Unintentional injury among young people worldwide 

A recent report appearing in the Journal of Adolescent Health, “The Health of Young People in a Global Context,” examines adolescent health in light of a shift in the leading cause of death among young people (ages 15-29) from infectious diseases to unintentional injury. Of world regions, only Africa, where AIDS is the number one killer of young people, and South America, where homicide and war rank first, deviate from this trend. The authors report that traffic-related fatalities are “by far the most prevalent” type of unintentional injury in most regions of the world, ranking first in 11 industrialized countries and becoming more of a threat among young people in low-income countries. For example, in Latin America (where unintentional injury is the third leading cause of adolescent death after homicide and war), between 1968 and 1983, adolescent mortality due to traffic crashes increased by 600 percent in Mexico, 250 percent in Venezuela, and 210 percent in Chile. Other types of unintentional injury include burns and poisonings, injury due to recreational and sports activities and falls and drowning.

Because low-income countries have large adolescent populations—over 85 percent of all young people reside in them, and that proportion is expected to increase in the coming years—trends in morbidity and mortality among young people in low-income countries offer insight into the general health crises facing low-income countries across the globe. In addition, the migratory patterns of young people, characterized by an influx of young laborers into cities, have shaped epidemiological trends. As the authors note, rural-to-urban migration predisposes young people to “significant behavioral health risks that stem from unemployment and poverty, such as violence, prostitution, sexually transmitted diseases, including HIV, and substance abuse.” While the authors do not draw attention to the link, there is most certainly a strong connection between rural-to-urban migration and increased traffic fatalities, as well.   

Although unintentional injury is named the leading cause of death among young people worldwide, other health issues—communicable disease, violence (including homicide and war, suicide and sexual abuse), reproductive health issues, and substance abuse—are dealt with more substantially in the adolescent health report, with a section devoted to each of these topics. The focus here on health risks traditionally considered the domain of public health professionals rather than on the emerging risks from traffic fatalities and other types of unintentional injury is worth noting.  
 

Are traffic fatalities a “disease of affluence”?

Understanding the factors that have contributed to the rise in traffic fatalities will help identify measures best suited to reversing this trend. Some have hypothesized that this phenomenon can be linked to a larger trend known as the "diseases of affluence," reflecting the seeming shift in patterns of mortality and disease as a country grows more prosperous. Overall, mortality rates drop, with infectious diseases becoming less of a threat. Initially, other types of disease or injury begin to replace them. For example, researchers identified a rise in cardiovascular mortality as the western world became more industrialized and more prosperous.  

But this interpretation falls short for traffic safety on a number of counts. A key consideration that it fails to address is the nature of the traffic risks in low- and middle-income countries and the character of the groups that are suffering the greatest burden. Both are starkly different from high-income countries. In a 2000 International Epidemiological Association study, "Economic development and traffic accident mortality in the industrialized world, 1962-1990," the authors point to findings that indicate that as wealth increases, so does the number of traffic deaths, but the correlation does not hold when the number of vehicles is considered. After adjusting for the variation in the number of motor vehicles in the population (traffic mobility), "there is a strong negative association between prosperity and the number of traffic deaths per motor vehicle (fatal injury rate)," the authors wrote. In other words, neither economic prosperity nor mobility rates alone, but a combination of these factors determines the rates of traffic mortality in a country, making the “disease of affluence” formulation too simplistic. 

The results confirmed that while the “disease of affluence” hypothesis is indeed too simplistic, it is not without some truth. Their findings indicated that when the industrialized countries surveyed were still at relatively low prosperity levels compared to those of today, an increase in wealth spurred an increase in traffic mobility. At these earlier stages of economic growth, industrialized countries did appear to be plagued by this “disease of affluence”—not simply by motor vehicle-related deaths, but also by cardiovascular mortality, as mentioned above. However, the findings also indicated that after prosperity reached a certain level, traffic mobility growth leveled off. At this point, the authors write, “increasing prosperity became protective against traffic accident mortality.” At this stage, “the number of traffic deaths per motor vehicle or ‘fatal injury rate’” declined. 

Data included traffic mobility, traffic mortality and the fatal injury rate (the number of traffic deaths per motor vehicle in the population). The shift whereby traffic mobility began to “level off” while prosperity continued to rise occurred in the second half of the 1970s. Furthermore, the researchers found that this shift occurred, on average, at the point when a country’s prosperity level reached the equivalent of about 3,000 international dollars per capita. Below this level, economic growth was accompanied by a continued rise in traffic mortality, while above this level prosperity became “protective against accident mortality.”

The authors suggest that the trend whereby the fatal injury rate declines after prosperity levels reach a certain mark may be due in part to improvements that generally accompany economic prosperity. Thus, while prosperity leads to greater mobility—which initially has negative effects—it “could stimulate adaptations” such as better transportation infrastructure and better medical care for the injured. According to the authors, “currently, in most industrialized countries the balance appears to be weighted in favor of the positive effects, as mobility growth has leveled off.” Still, they caution that because the majority of countries worldwide has not reached the 3,000 dollar mark, all else being equal, “an enormous increase in deaths and injuries due to traffic crashes could still be expected.”

The results of this study suggest that a closer examination is needed of the specific nature of the adaptations that seem to accompany higher levels of economic prosperity in industrialized countries, how quickly these adaptations come about, and—most importantly—how these adaptations affect traffic safety outcomes.

Photo by Markus A. Jegerlehner [via bigfoto.com]