New care models have been defined in order to manage the increasing impact of chronic conditions. These models pose several technology-oriented challenges for home-based continuous care, requiring assistance services based on collaboration among different stakeholders: health operators, patient relatives, as well as social community members. This work describes an ontology-based context model and a related context management middleware providing a reusable and extensible application framework for monitoring and assisting patients at home. It provides flexible instruments for patient health status and social context representation, as well as reasoning mechanisms for alarm situation handling.