Beem, M. O. (Dept. Pediatrics, Univ. of Chicago, Chicago, III. 60637). Acute respiratory illness in nursery school children: a longitudinal study of the occurrence of illness and respiratory viruses. Amer. J. Epid., 1969, 90: 30–44.—Children, aged three to five years, attending a day care nursery school were observed from November, 1962 to August, 1963 to determine the incidence of respiratory infections and the role played in these by influenza, parainfiuenza, respiratory syncytial, adeno and picoma viruses. The observed incidence of acute illness considerably exceeded that recorded for children of a similar age in household settings, and acute respiratory illness accounted for the overwhelming majority of the total illness experienced by the children. Infections with adeno, para-influenza and influenza viruses were identified, but to the extent that could be determined by virus isolation these did not appear to spread widely through the group. Introduction of respiratory syncytial (RS) virus resulted in extensive virus spread and illness, in spite of the fact that serotogic evidence indicated the majority of the children had experienced previous RS virus infections. Rhinovirus infections were the most frequently identified cause of respiratory illness accounting for a larger portion of the acute respiratory illness of defined etiology than all other viruses combined. These infections occurred in all seasons of the year and were caused by 14 different rhinovirus serotypes. There was great variation in the extent to which rhinoviruses spread. Half of the serotypes introduced into the group underwent no detected spread. The other seven spread to one or more children, and three of these spread quite extensively, infecting from 42 to 77% of the children. There was a clear association of respiratory illness with rhinovirus shedding.