From the French surveiller, “to watch over,” public health surveillance has its roots in 14th-century Europe. In an early form of surveillance, in approximately 1348, the Venetian Republic appointed guardians of public health to detect and exclude ships that carried plague-infected passengers. In 1662, English demographer John Graunt analyzed the mortality rolls in London and described a system to warn of the onset and spread of plague. Until the 1950s, “surveillance” referred to monitoring a person exposed to a disease; the current concept of surveillance as monitoring disease occurrence in populations was promoted by Alexander Langmuir of the Communicable Diseases Center (now the Centers for Disease Control and Prevention).