Anything symptomatic relates to the symptoms of a disease. If you're symptomatic, you might be sick.
A symptom is a sign of a disease or illness. Symptoms of a cold include a stuffed nose and cough. So if you have a cough, you're symptomatic. Being symptomatic means you're showing symptoms of something. Sometimes you can be symptomatic and not have an illness: the doctor might not be sure why you're having headaches, for example.