o Are highly infectious, and therefore have outbreak potential (e.g. food-borne illnesses, measles, out-of-season influenza, meningococcal disease) o Have a short incubation period (and are therefore likely to present while the MG is still occurring) o Are difficult to treat or manage (e.g. XDR-TB) o Have modes of transmission likely to be enhanced in a mass gathering situation (e.g. meningitis, gastrointestinal and respiratory diseases) o May cause severe illness and require investigation and/or the application of control measures (such as quarantine), even for a single case o Are known to be of particular risk for use as bioterrorism agents Timeframe for effective prophylaxis of exposed asymptomatic persons (incubation period of disease)