An epidemic is the rapid spread of an infectious disease, usually in a particular area over a short period of time. E pidemiologists look for these additional key features a high number of infections in relation to the expected number. Endemic diseases (like influenza) return every year but usually at a low and predictable rate. spread accelerated by person-to-person transmission a rapidly increasing morbidity rate (proportion of the population with disease) a population that extends beyond shared accommodation (not a cruise ship, for example, where the world outbreak would be used.) For endemic diseases an epidemic can be clearly marked on a statistical chart - with a sudden rising curve . Here the data from hospital visits in the US suggests a possible influenza epidemic in the winter of 2007/8 (credit: modification of work by Centers for Disease Control and Prevention from ' The language of epidemiology ') With a new pathogen, it is more difficult to identify the start
