More and more forums, such as Slashdot ou Stack Exchange, offer reputation systems based on collaborative votes of postedmessages. Indeed, users can give a score to eachmessage according to its relevance or usefulness. However, these voting functionalities are not used in many online communities such as health forums. In these forums, users prefer posting a new message (reply) where they express agreement or thanking about relevant posts rather than pressing a vote up button. In this work, we suggest to use these hidden expressions of trust in order to estimate user reputations in online forums.