• Reporting/notification by states parties to WHO: notification to WHO is required for all cases of (i) certain specified diseases, and (ii) all events of sufficient seriousness according to at least two of the following four criteria, regardless of the particular disease or risk: (1) seriousness of public health impact of an event; (2) unusual or unexpected nature of an event; (3) risk of international spread of a disease; (4) risk of implementation of international restrictions on travel or trade.