Injured patients who had to travel an average 13 minutes longer to reach a hospital trauma center because a facility nearer to home had closed were more likely to die of their injuries in the hospital, according to a new California study.

The report found their risk of dying was 21 percent higher than that of patients with similar injuries whose average drive time to a trauma center hadn’t changed.

The patients whose trips got longer were also more likely to be younger and poorer, more likely to be black or Hispanic and more likely to be uninsured or covered by Medi-Cal, the government health plan for the poor in California, the study found.

“Hospitals in affluent areas fight to open trauma centers,” because they can charge steep fees for the services and even turn a profit, said Dr. Renee Y. Hsia, lead author of the study and an associate professor of emergency medicine at University of California, San Francisco.

“But if you’re in a poor area with a lot of violence, these trauma patients pour in and you provide a lot of high intensity care and you’re not reimbursed — those hospitals cannot survive.”

The findings suggest that the closing of trauma centers in urban areas in particular may be contributing to racial and economic health disparities, she said.

“Because we have a market-driven approach to health care, certain services and facilities are available to huge segments of the population, while other segments don’t have access to them,” Hsia said. “This is what happens in a market. Everyone thinks health care is a benevolent service, but it is very much a profit-making industry, and hospitals act like economic entities.”

The research, published Thursday in The Journal of Trauma and Acute Care Surgery, was supported by the UCSF Clinical and Translational Science Institute and the Robert Wood Johnson Foundation Physician Faculty Scholars Program.

While trauma center closures have accelerated in recent decades, those operated by public hospitals and urban hospitals are more likely to incur losses because of high operating costs and falling levels of reimbursement, studies have found. Hospitals serving areas with large minority populations were nearly twice as likely to close their trauma centers. In California between 1999 and 2009, the period studied by the researchers, three Level I and Level II trauma centers closed, while 10 centers opened, mostly in affluent areas, Hsia said.

For the study, researchers looked at more than one-quarter of a million adult visits to trauma centers in California between 1999 and 2009.  They compared the risk of dying in the hospital for the 5,122 trauma patients whose drive time to a center had increased after the closure of a nearby center with the risk for 266,023 patients whose travel time had stayed the same.

Patients whose drive time to the nearest trauma center averaged 47 minutes were more likely to die in the hospital than those whose drive time stayed constant at 34 minutes on average.  Injured patients whose closest trauma center had shut down were at greatest risk during the first two years after the closure, when their odds of dying in the hospital were 29 percent higher than for similar patients who had a center closer to their home.

The opposite also held true: Patients whose travel time to a trauma center decreased were 17 percent less likely to die than patients whose travel time stayed constant, the researchers found.

Since “it is not feasible to put a trauma center on every street corner” because of their cost and the relationship between volume and outcomes, the study called for health administrators and policymakers to work strategically “to ensure equitable access.”