Poliovirus is a very contagious virus that can spread easily from person to person. In fact, when a person is infected with poliovirus, it is expected that polio transmission among susceptible household contacts will occur in nearly 100 percent of children and over 90 percent of adults.

Poliovirus is a single-stranded RNA virus from the family Picornaviridae and genus enterovirus.

Poliovirus only infects humans, and it is more common during summer months in temperate climates. In tropical climates, there is no seasonal pattern. The poliovirus is rapidly inactivated by heat, formaldehyde, chlorine, and ultraviolet light.

What Causes Polio? -- Transmission

Polio is very contagious. When a person is infected with poliovirus, the virus resides in the intestinal tract and mucus in the nose and throat. Poliovirus is usually spread through contact with stool of the infected person (known as fecal-oral transmission). Less frequently, poliovirus is spread through contact with infected respiratory secretions or saliva (oral-oral transmission).

Following polio transmission, a person does not become immediately sick. A person who is infected with polio can spread polio about 7-10 days before symptoms begin. A person can continue to spread polio for about three to six weeks after the beginning of polio symptoms. However, a person is most contagious for the 7-10 days after symptoms of polio have begun.

(Click Polio Incubation Period for more information on this period between a person becoming infected with poliovirus and the beginning of polio symptoms.)