The Centers for Medicare and Medicaid Services (CMS) classified emergency departments into two types: Type A, the majority, which are open 24 hours a day, 7 days a week, 365 days a year; and those who are not, Type B. Many US emergency departments are exceedingly busy. A study found that in 2009, there were an estimated 128,885,040 ED encounters in US hospitals. Approximately one-fifth of ED visits in 2010 were for patients under the age of 18 years. Most encounters (82.8 percent) resulted in treatment and release; 17.2 percent were admitted to inpatient care.