It stands to reason that when a hospital emergency room closes, people in the surrounding neighborhood suffer. But how much? A new study quantifies the impact in California, finding that patients affected by ER closings were 5 percent more likely to die after being admitted to a hospital than were patients who didn’t lose ERs in their neighborhoods.

The authors of the study, published Monday in the journal Health Affairs, couldn’t say exactly how the disappearance of emergency rooms translated into higher mortality for hospital patients. Fewer ERs lead to longer wait times for treatment. It also means patients have to travel farther to get emergency room care, and that may prompt some to stay home. All these factors force patients to wait longer – and perhaps get sicker – by the time they are admitted to a hospital.

Understanding the implications of ER closings is important, since they have been disappearing for years. The number of hospital emergency departments in the United States fell from 4,884 in 1996 to 4,594 in 2009, a 6 percent decline. Meanwhile, the number of patient visits increased from 90 million to 136 million, a 51 percent increase. Figures like these prompted the Institute of Medicine to declare that emergency departments were “at the breaking point” back in 2006.

For the new study, three researchers from Harvard Medical School, the University of California, San Francisco, and the Ecologic Institute in San Mateo, Calif., examined data from the California Office of Statewide Health Planning and Development to see how many hospital emergency rooms were in operation and what happened to the patients they treated.

From 1999 to 2010, 26 California hospitals that had emergency rooms closed, and 22 others closed their emergency rooms but remained open, according to the study. Each of those 48 hospitals affected a geographic area that the researchers defined by the ZIP codes of the patients who used the facilities.

During the years studied, more than 16 million patients who visited California ERs were admitted to the hospitals. Twenty-five percent of them were from neighborhoods affected by an ER closing, and 75 percent were not. (Emergency rooms are required by law to treat all patients regardless of how sick they are or whether they can pay for their care.)

Overall, patients who were African American, Latino, women or adults under the age of 65 were more likely to have suffered the loss of an ER in their communities, the researchers found. So were patients who were uninsured or were covered by Medicaid, the federal insurance program for low-income Americans.

The effect of ER closings was greatest on nonelderly adults (those between the ages of 18 and 64). Among patients in that age group, those who lived in an affected area were 10 percent more likely to die after being admitted to the hospital, compared with patients who didn’t lose ERs.

Elderly patients (those 65 and older) appeared more likely to die after being admitted to hospitals if they were from an affected area, but the difference wasn’t large enough to be statistically significant.

When the researchers focused on patients from neighborhoods that lost ERs in the previous two years, they found that affected patients were 4 percent more likely to die during their hospital stay than were patients who hadn’t lost ERs so recently.