Smallpox usually requires fairly prolonged face-to-face contact to spread. It's most often transmitted through the air by droplets that escape when an infected person coughs, sneezes or talks. In rare instances, airborne virus may spread farther, possibly through the ventilation system in a building, infecting people in other rooms or on other floors. Smallpox can also spread through contact with contaminated clothing and bedding, although the risk of infection from these sources is slight.

Aug. 10, 2011

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