syndrome is usually used to describe a cluster of symptoms, when the etiological (pathogenic) agent is not yet known.

Dear Dr. Ghiasi,

Thanks for your valued response and scientific explanation but it seems that your answer was located opposite to Dr. Rachel response!

According to mentioned responses EUS should be converted to Disease because its causative agents were recognized.

Am I right?

A syndrome is a bunch of symptoms that often occur together. Many diseases can cause the same syndrome. for example, fever and a sore throat  is a very common syndrome. It can be caused by diseases as different as bacterial pharyngitis, the flu and cancer of the larynx.

Dear Dr. Haghighi,

Thanks a lot for your valued comments.

According to definition of syndrome in Oxford Dictionary:

"A group of symptoms which consistently occur together, or a condition characterized by a set of associated symptoms."

So would you think about this definition in EUS?

I would only suggest changing the name from syndrome to disease if Koch's Postulates could be fulfilled, for example with the bacterial pathogens described by Dr. Ghiasi. For example, what if one of the two bacteria Dr. Ghiasi mentioned was the etiological agent and the other was an opportunist? naming both as causative of a disease would be erroneous.

A disease can be defined as a health condition that has a clearly defined reason behind it.

A syndrome (from the Greek word meaning ‘run together’) however, may produce a number of symptoms without an identifiable cause.