In medicine, any disease is classified asymptomatic if a patient tests as carrier for a disease or infection but experiences no symptoms. Whenever a medical condition fails to show noticeable symptoms after a diagnosis it might be considered asymptomatic.
Infections of this kind are usually called subclinical infections. Diseases such as mental illnesses or psychosomatic conditions are considered subclinical if they present some individual symptoms but not all those normally required for a clinical diagnosis. The term clinically silent is also found. Producing only a few, mild symptoms, disease is paucisymptomatic. Symptoms appearing later, after an asymptomatic incubation period, mean a pre-symptomatic period has existed.
Knowing that a condition is asymptomatic is important because:
An example of an asymptomatic disease is cytomegalovirus (CMV) which is a member of the herpes virus family. "It is estimated that 1% of all newborns are infected with CMV, but the majority of infections are asymptomatic." (Knox, 1983; Kumar et al. 1984) In some diseases, the proportion of asymptomatic cases can be important. For example, in multiple sclerosis it is estimated that around 25% of the cases are asymptomatic, with these cases detected postmortem or just by coincidence (as incidental findings) while treating other diseases.
Asymptomatic conditions may not be discovered until the patient undergoes medical tests (X-rays or other investigations). Some people may remain asymptomatic for a remarkably long period of time, such as people with some forms of cancer. If a patient is asymptomatic, precautionary steps are ineffective and should not be taken. The patient should continue to seek treatment for the main disease they are suffering from currently.
Some diseases are defined only clinically, like AIDS being the result of HIV infection. Therefore, it makes no sense to speak about "asymptomatic AIDS". This concept of clinically defined diseases is related in some way to the concept of syndrome.
These are conditions for which there is a sufficient number of documented individuals that are asymptomatic that it is clinically noted. For a complete list of asymptomatic infections see subclinical infection.
Millions of women reported lack of symptoms during pregnancy until the point of childbirth or the beginning of labor; they didn't know they were pregnant. This phenomenon is known as cryptic pregnancies.