Mathematical models dealing with childhood viral infections consider the spread of disease according to the law of mass action. This law states that there are random encounters (or contacts) among susceptible and infectious individuals. Therefore, mathematical descriptions of the transmission of infections are heavily dependent on the assumptions concerning the contact rate. In order to develop an age-structured contact rate model, a pattern of contacts among individuals in a community is developed by stochastic processes. (C) 1999 Elsevier Science Ltd. All rights reserved.2983948