Needle Sharing Infections among Heterogeneous IVDUS

 This paper begins with an alternative derivation of the coefficients in a known probability generating function (pgf ), namely that for the number of new infectives generated in a random allocation model of needle sharing among i infectives and n susceptibles. The expectation and variance of the number of new infectives are derived. The pgf for such a model is then obtained when there are types of susceptibles; the probabilities of generating new infectives are found for , where the infectives have preferential probabilities p and q for type 1 and 2 susceptibles respectively. The case of variable susceptibilities is also considered, and the paper concludes with some remarks on the pgf method. Received 21 February 2001; in final form 15 September 2001