A time-frame during which people or animals suspected of carrying a contagious disease are isolated to prevent spreading the disease to others in the outside environment. The first use of quarantine was in the 14th century, during the time of the plague where ships arriving in port were kept offshore for 40 days. Today, quarantine is routinely applied to dogs or other animals that are imported from one country to another. It can also be applied to people with certain communicable diseases such as the H1N1 flu virus.