Social distancing is a term applied to certain nonpharmaceutical infection control actions that are taken by public health officials to stop or slow down the spread of a highly contagious disease. The objective of social distancing is to reduce the probability of contact between persons carrying an infection, and others who are not infected, so as to minimize disease transmission, morbidity and ultimately, mortality. Social distancing is most effective when the infection can be transmitted via droplet contact (coughing or sneezing); direct physical contact, including sexual contact; indirect physical contact (e.g. by touching a contaminated surface such as a fomite); or airborne transmission (if the microorganism can survive in the air for long periods). Social distancing may be less effective in cases where the infection is transmitted primarily via contaminated water or food or by vectors such as mosquitoes or other insects, and less frequently from person to person. One of the earliest references to social distancing dates to the seventh century BC in the Book of Leviticus, 13:46: "And the leper in whom the plague is...he shall dwell alone; [outside] the camp shall his habitation be." Historically, leper colonies and lazarettos were established as a means of preventing the spread of leprosy and other contagious diseases through social distancing, until transmission was understood and effective treatments were invented.