there's a discussion of this point here
Condition is perhaps the least specific, often denoting states of health considered normal or healthy but nevertheless posing implications for the provision of health care (eg, pregnancy). The term might also be used to indicate grades of health (eg, a patient might be described as in stable, serious, or critical condition). While this term is often used in medical discussions to specifically indicate the presence of pathology or illness, Dorland’s Illustrated Medical Dictionary provides no definition of the term used in this sense. Merriam-Webster’s Collegiate Dictionary, however, defines condition as “a usu. defective state of health,”2(p258) and the Oxford English Dictionary similarly opines that it denotes “[a] state of health, esp. one which is poor or abnormal; a malady or sickness.”1(p309)
where disease refers to a condition where usually there is a well established pathological process.