According to the U.S. Department of State Trave

According to the U.S. Department of State Travel website:
 

Obtaining medical treatment and hospital care abroad can be expensive, and medical evacuation to the U.S. can cost more than $50,000. Note that U.S. medical insurance is generally not accepted outside the United States, nor do the Social Security Medicare and Medicaid programs provide coverage for hospital or medical costs outside the United States. 

 

There are health insurance policies both for short term trips and longer stays abroad that you can purchase which will provide full coverage outside the US.