What killed 488,015 people from 1999 to 2012? A mega-crunch of data from the National Center for Health Statistics against national census data suggests that poverty may be to blame.
The study, published last week in PLOS One, looked at every U.S. fatality from unintentional injuries and income data for the entire U.S. population, for the 14-year period, down to the county level.
“This is national data — the highest quality data you could possibly have,” says investigator Eric Fleegler, MD, MPH, an emergency physician physician at Boston Children’s Hospital who is interested in socioeconomic factors in health. “It’s unusual to have data of this breadth and depth.”
Unintentional injuries are already known to be the fifth largest cause of death in the U.S., and these mortalities have been rising over the past decade. At the same time, more people are living in areas with high poverty levels.
Are these two trends connected?
Fleegler, together with Rebecca Karb, MD, PhD of Brown University’s Alpert Medical School and S.V. Subramanian of the Harvard T.H. Chan School of Public Health, set out to answer that question, They defined poverty, per federal guidelines, as an annual income of roughly $25,000 or less for a family of four, and looked at six categories of unintentional injury: motor vehicle crashes, falls, accidental discharge of a firearm, drowning, poisoning and exposure to fire or smoke.
Nationwide, the researchers found:
• Age-adjusted mortality from unintentional injuries rose 7 percent from 1999 to 2012, from 35.2 to 38.6 per 100,000 population.
• The greatest increases were for falls (from 4.8 to 8.1 per 100,000) and poisonings (from 4.3 to 11.4 per 100,000).
• Analyzed by race, unintentional fatalities rose for whites but fell among blacks, Hispanics and other races.
• By age, the 45-64 age group saw the largest increase.
So what about poverty? To get at that question, the researchers used census data to stratify counties by poverty rate (the percentage of residents living in poverty).
In 1999, high-poverty counties (poverty rate 20 percent or higher) had 66 percent more unintentional fatalities per 100,000 population than low-poverty counties (poverty rate below 5 percent).
This difference got worse with time: by 2012, the difference in fatalities between high- and low-poverty counties had increased to 79 percent.
- Rates of all types of fatal injury, except for falls, increased markedly with county poverty levels. Over time, however, deaths from falls, poisoning and drownings increased the most in higher-poverty areas.
- In a multivariate analysis, adjusting for age, sex, race/ethnicity and urbanism, people in the poorest counties in 1999 were 49 percent more likely than those in the least-poor counties to die from unintentional injury. By 2012, this difference had surged to 72 percent.
Finally, the researchers calculated that of the 1.6 million unintentional deaths from injury that took place in the 14-year period, 33 percent — 488,015 people — would not have died had they lived in a county with a low poverty rate. Like the other stats, this fraction got higher over time, rising from 22 percent in 1999 to 35 percent in 2012.
What the data tell us, says Fleegler, is that not only are more and more unintentional deaths associated with poverty, but the effects of poverty are getting worse over time.
“We don’t know the reasons,” he says. “A lot of things have been looked at in the literature: less seatbelt use; a built environment that is physically less safe; a greater number of guns that are not stored safely; worsening opioid epidemics. Overall, though, I think what’s driving it is that more people are exposed to poverty.”
This means that even “non-poor” residents are affected when the surrounding area becomes poorer. The researchers suggest that future studies examine what is happening in the social and physical environment in poorer areas to make death from injury more likely, and that injury reduction interventions focus on areas of high or increasing poverty.
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