Transmission of chickenpox in a school setting prior to the observed exanthem.

An epidemic of chickenpox in a class is described. Four children were able to transmit infection prior to the time their rash was observed by their parents. A fifth child was known to have attended school while he had localized varicelliform lesions that were present for 2 days prior to the appearance of the generalized exanthem. It cannot be ascertained whether some of the other children may have had similar lesions that were not observed at the time they attended school. The first classroom case was observed prospectively so that the time of rash was fairly well established. Although he apparently transmitted infection prior to the onset of rash, virus could not be isolated from the respiratory secretion of this child on the day he presumably infected his classmate. Virus was not found in his respiratory secretions or those obtained from his two siblings before or after the onset of rash, although it was recovered from vesicular fluid.