Here is a list of health reasons why someone would be denied a visa:
(1) having a communicable disease of public health significance (HIV/AIDS)
(2) having a mental or physical disorder and behavior associated with the disorder that may pose, or has posed, a threat to the property, safety, or welfare of the alien or others
(3) have had a physical or mental disorder and a history of behavior associated with the disorder, which behavior has posed a threat to the property, safety, or welfare of the alien or others and which behavior is likely to recur or to lead to other harmful behavior
(4) drug abusers and addicts
Website --->
http://travel.state.gov/visa/frvi/ineligib...ities_1364.html