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Photo by  CDC  on  Unsplash It is often assumed that the bubonic plague (black death) spread across Europe because the authorities did not understand the concept of contagion. In fact, it was widely understood that an infected person would pass their disease to others. What was not known was the precise transmission mechanism or what you needed to do to avoid contagion. It was obvious, however, that the disease was manifesting itself in particular localities. The key to prevention was isolation. You needed to keeping infected persons out your town, city or community. Who first used the term? In the 1340s the Venetian authorities in charge of the port city of Ragusa (Dubrovnik) issued the first quarantine measures. This was aimed  at ensuring that infected visitors did not mix with the rest of the population.  The edict established an isolation period of trentino giorni (30 days). This applied to anyone arriving from an area known to be affected by bubonic plague. This example

Covid test vial  Photo by  Vincent Ghilione  on  Unsplash Seroprevalence is the level of a pathogen (e.g. the virus Covid-19) found in a particular population - a country, city or region for example. This is measured by administering blood test to as wide a sample of that population as is feasible. Testing The accuracy of seroprevalence is dependent on a number of factors including the size of the sample tested as a proportion of the general population Photo by  Colin D  on  Unsplash the representative nature of that population in terms of age, sex, socio-economic conditions, ethnicity, size of household, number of social interactions, occupation etc. the accuracy of the tests, especially if these are physically difficult to administer. Covid-19 tests are quite physically intrusive as they require a throat swab. the accurate record keeping of the testers the potential for cross-contamination the estimated number of false positives and false negatives. Medical

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