Seniors’ trips to the emergency room are rising in frequency faster than any other age group, say researchers at George Washington University. Investigators said they were unsure why the rates are up so dramatically, but they estimate that by 2013, yearly visits could top 11 million. That would be a 72% rise from 2003 levels (6.4 million visits).

One possible explanation is the number of uninsured seniors who became eligible for Medicare after turning 65 who could not previously afford treatments, expert said.

The study, which examined emergency room visits by all age groups between 1993 and 2003, found that the rate of visits by the 65-to-74 cohort (34%) grew more than twice as fast as that for the 50-to-64 group (16%) and much faster than the 22-to-49 group (19%). The report was published Wednesday in The Annals of Emergency Medicine.