Whether, and how far, a society may detain or confine healthy people who have been exposed to a contagious disease, against their will, to stop them from spreading it before they fall sick — a contested choice that sets the collective claim to safety from an epidemic against the individual claim to liberty, bodily autonomy, and due process, and that has repeatedly been turned against the poor and feared minorities under a health pretext.
The word comes from a number: quaranta, the Italian for forty. But the practice began earlier, and shorter. In 1377, Ragusa — the Adriatic port now called Dubrovnik — ordered arrivals from plague-struck places to wait thirty days apart, a trentino; Venice later stretched the wait to the forty days that gave quarantine its name. Ships sat at anchor before anyone could land, in the hope that any plague aboard would burn itself out at sea. It was a brutal instrument and a logical one. It confined people who looked healthy but might have been exposed, on the chance that some carried death without knowing it. That is the bargain quarantine has always offered. It can halt an epidemic before a cure exists, and it can just as easily become a tool of fear, turning the sick and the merely foreign into prisoners. The same power that stopped the plague at the harbor has, again and again, been aimed at whoever a frightened society already wished to shut out.