This originally appeared on Time.com.
People who run marathons go through intense training before enduring the physically grueling 26.2-mile event—so it’s little wonder . But on marathon days, the event can also create unexpected problems for non-runners who need urgent medical care.
In a new report published in the New England Journal of Medicine, researchers found that road closures and traffic disruptions on marathon days can lead to delays in emergency care that can cost people their lives.
Dr. Anupam Jena, from the department of health care policy at Harvard Medical School and Massachusetts General Hospital, and his colleagues analyzed data from Medicare claims for hospitalizations for in 11 cities that hosted marathons from 2002 to 2012. They compared the death rates of these people on marathon days to those a few weeks before and after the marathon. People who had heart attacks on marathon days had a 13% higher rate of death than people on other days. Ambulances also took 4.4 minutes longer on days marathons were run.
“We were expecting to see there would potentially be delays in care,” says Jena, “but not necessarily increases in mortality. It’s difficult to influence mortality; you would have to have substantive delays in care.”
Road closures, detours and other changes in traffic patterns were dramatic enough to cause delays that could affect a person’s chance of surviving a heart attack, the team found. Over a year, marathons could contribute to an additional four deaths, based on the 30-day mortality rate calculations. The effect remained strong even after they adjusted for the possibility that more people visit a city hosting a marathon, and therefore statistically there may simply be more heart events. The researchers also made sure that hospitals and emergency services were not short-staffed or overburdened with the added volume of requests. All of these factors were similar on marathon and non-marathon days.
The disruption in traffic during a marathon is the primary reason for delays in care, Jena says. That’s good news because it’s a fixable problem; marathon planners can ensure that access to hospitals is not congested and affected by the race route.
The other lesson from the study is useful for people in need of medical attention. A quarter of the people in the study chose not to call an ambulance and instead drove themselves to the hospital—perhaps because they thought that emergency services were tied up with the marathon—and these people seemed to account for most of the higher mortality on marathon days, says Jena. That may be because they were forced to take more circuitous routes to reach the hospital, he says. “They don’t experience the four-minute delays of ambulance transport; they’re experiencing much larger delays because they are trying to drive themselves.”
Even with the delays, ambulances were the best form of transportation to the emergency room. “Anybody thinking of driving to the hospital themselves on the day of a major public event should pick up the phone and call 911,” Jena says.