A person infected with parvovirus B19 is contagious during the early part of the illness, before the rash appears. By the time a child has the characteristic “slapped cheek” rash of fifth disease, for example, he or she is probably no longer contagious and may return to school or child care center. This contagious period is different than that for many other rash illnesses, such as measles, for which the child is contagious while he or she has the rash.

Parvovirus B19 has been found in the respiratory secretions (e.g., saliva, sputum, or nasal mucus) of infected persons before the onset of rash, when they appear to “just have a cold.” The virus is probably spread from person to person by direct contact with those secretions, such as sharing drinking cups or utensils. A susceptible person usually becomes ill 4 to 14 days after being infected with the virus, but may become ill for as long as 20 days after infection.

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