Colds are readily transmissible to human volunteers by intranasal administration of human coronaviruses. After an incubatioi*! period of 2-5 days, symptoms develop in about half of those inoculated, and virus is shed for about a week.
Coronavirus colds occur mainly in the winter and early spring. A longitudinal study in the United States indicated that large outbreaks of either 229E or OC43 infection tend to occur with a periodicity of 2-4 years. Adults are affected as well as children because acquired immunity is so ephemeral. Overall, it is estimated that coronaviruses are responsible for about 15% of all colds.
The role, if any, of enteric coronaviruses and/or toroviruses in human gastroenteritis remains uncertain. Transmission is presumably by the fecal-oral route.
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