A measles epidemic in a modern suburban elementary school In upstate New York In spring, 1974, is analyzed in terms of a model which provides a basis for apportioning the chance of infection from classmates sharing the same home room, from airborne organisms reclrculated by the ventilating system, and from exposure In school buses. The epidemic was notable because of lts explosive nature and lts occurrence In a school where 97% of the children had been vaccinated. Many had been vaccinated at less than one year of age. The Index case was a girl In second grade who produced 28 secondary cases in 14 different classrooms. Organisms reclrculated by the ventilating system were strongly Implicated. After two subsequent generations, 60 children had been Infected, and the epidemic subsided. From estimates of major physical and biologic factors, It was possible to calculate that the lndex case produced approximately 93 units of airborne lnfection (quanta) per minute. The epidemic pattern suggested that the secondaries were less Infectious by an order of magnitude. The exceptional Infectiousness of the Index case, lnadequate Immunization of many of the children, and the high percentage of air reclrculated throughout the school, are believed to account for the extent and sharpness of the outbreak.
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