There is no specific suffix meaning infection. The suffix -itis applies to any condition that involves inflammation. Arthr/itis is an example of an inflammatory condition that doesn't involve infection.
Since all infections produce inflammation, and there is no suffix for infection, the suffix -itis is used to refer to infections. So, while it is usually safe to assume that when someone has appendicitis, there is infection present in the appendix, the term appendic/itis only indicates with certainty that there is inflammation present, which may or may not involve infection.
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