Approximately 2.3 million ED visits (2.0 percent of all visits) were made by persons who had been hospitalized with the last 7 days. This corresponds to 68 ED visits per 1,000 live hospital discharges. About 10 percent of patients at these ED visits presented with medical or surgical complications that may have been related to their recent hospitalization.
Uninsured persons were nearly three times as likely as those privately insured to make an ED visit follwing hospital discharge. You can read more on here.
NCHStats 
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