Quarantine: an ancient measure back in vogue

Quarantine is a period of forced isolation to which are subjected apparently healthy individuals (in some cases even animals) considered possible carriers of infection, in order to contain the spread of a disease in a given area. The word "quarantine" (from Venetian dialect) indicates forty days, the typical duration of the isolation to which ships and sailors from areas affected by the plague in the fourteenth century were subjected, before entering the lagoon of the Republic of Venice.

Between 1348 and 1359, in fact, the so-called "black plague" exterminated about 30% of the European and Asian population. For this reason, in 1377, passengers of a vessel docked at the port of Ragusa (today Dubrovnik, in Croatia) were forced to wait for a thirty-day observation period, later extended to forty days, before being able to go ashore, in order to make sure that nobody could spread the disease in the city.

Quarantine does not necessarily last 40 days: its duration depends on the incubation period of the disease (i.e. the maximum period of time that elapses between contagion and the development of clinical symptoms). For example, the incubation period for measles is between 9 and 15 days; that of MERS-CoV, a coronavirus that has caused hundreds of cases in the Middle East, is 5-7 days; the flu has an incubation period of a few hours to a few days.

The most accurate estimate of the maximum duration of the incubation period is of fundamental importance to support the planning of public health interventions, including active surveillance, infection control and epidemic modeling.

For COVID-19, the median of the incubation time is estimated to be between 5 and 6 days, ranging from 2 to 14. A recent study by the Johns Hopkins Bloomberg School of Public Health, published in the Annals of Internal Medicine journal, showed that the 97.5% of people develop symptoms of SARS-CoV-2 infection within 11.5 days of exposure; the recommended quarantine (14 days) therefore appears to be a reasonable period of time.

Although little used in the recent past, quarantine is a measure provided by the International Health Regulations (adopted by the World Health Organization, WHO) for some diseases such as plague, cholera, yellow fever and SARS. The characteristics of the COVID-19 pandemic, and in particular its relatively long incubation period, have suggested its extensive use to contain the spread of the virus, in particular for those who came into contact with proven cases of COVID-19 (isolations trustees) or for areas with a high concentration of cases (red areas).

Quarantene, lazzaretti, cordoni sanitari...presso la Biblioteca San Raffaele è esposta la mostra "Contagio": sei isole tematiche per raccontare la paura delle pestilenze nei secoli con alcuni documenti antichi del Fondo D'Agostino. Scopri di più

Immagine nel testo: "Malta: view of the quarantine area". Etching by M-A. Benoist, c. 1770, after J. Goupy, c. 1725.