Epidemic intelligence (EI) carried out at ECDC refers to the systematic process of collection, validation and analysis of information about potential public health events from a virtually unlimited amount of sources. The purpose of the EI process is to speed up the detection of public health events in order to allow the implementation of timely response actions after an adequate risk assessment. The EI process includes the use of routinely collected official data provided by national health authorities about infectious diseases through indicator-based surveillance (IBS) as well as the monitoring of additional unverified information about potential public health events through event-based surveillance (EBS). ECDC EI activities during mass gathering focus mostly on the EBS component and in particular on the processing of web-based information. To do so, we use advanced web-technologies defined as EBS systems which are able to gather, filter and classify public health information online. MedISys is among the EBS systems most frequently used for EI purposes at ECDC because of its extreme flexibility and the possibility of its customisation. The system which was developed in 2006 by the European Commission?s Joint Research Centre (EC-JRC) is capable of screening selected web-sources, including online media and government websites, using a multilingual triggering method based on keyword definitions for more than 40 languages. The information is classified and geo-located in a user interface accessible on the web.