If something bad is symptomatic of something else, it is caused by the other thing and is proof that it exists.

Jealousy within a relationship is usually symptomatic of low self-esteem in one of the partners. 恋爱关系中嫉妒情绪的产生通常表明其中一方不够自信。

showing symptoms of a particular disease

symptomatic AIDS patients 已显露症状的艾滋病患者

symptomatic influenza 带症状的流感

A doctor who had treated an Ebola patient may have been symptomatic when he boarded the plane. 一位曾治疗过埃博拉患者的医生在登机时可能已显露症状。