When you come to the U.S. with hopes of staying here a while, you will be expected to take an immigration medical exam. Despite your personal perceptions of your own health, the immigration officers will not take your word for it. There are several good reasons why the U.S. Immigration Office expects you to have a medical exam.
1. Avoid Re-Introducing Eradicated Health Problems
There have been almost no cases of polio, measles, typhoid, and other life-threatening communicable diseases in the U.S. for decades. Most of the cases that are reported are the direct result of foreign carriers of these diseases. When you plan to stay in the U.S., you have to go through a medical exam to make sure you are not carrying these previously eradicated diseases and to make sure you are not susceptible to them.
2. Clear You of Trying to Infect U.S. Citizens
Bio-terrorists often choose to be the carriers of deadly diseases. They will kamikaze a nation by injecting themselves with deadly pathogens, and then get on a plane for the targeted country. By requiring a health exam to enter the U.S., both the CDC and Immigration can prevent bio-terrorists from spreading these infections and prevent hundreds or potentially thousands of U.S. citizens from getting sick or dying.
3. Alert You to Serious Health Conditions
You may feel fine, but many health conditions can go undetected for years. HIV, some forms of cancer, and hepatitis are just three examples of serious health conditions that you may not feel or see for years. Since the U.S. is unlikely to provide you with free healthcare during the duration of your visit (especially for a serious health condition), you may want to return to your native country to get treatment.
4. Prevent Lawsuits Against Americans
Other immigrants might come to the U.S. with a condition that is exacerbated by manual labor, or that causes them to get into serious accidents (e.g., a severe seizure disorder). Then they sue American employers for the money. By screening you for such health issues and physical challenges, the opportunity for these events, and the possible lawsuits that could ensue, are decreased. (That is not to say you would be such a person, but Immigration likes to make sure that American citizens are protected against such incidents. Ergo, every immigrating person is screened for health problems that could lead to such financially damaging behavior.)