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 k > 1 types of susceptibles; the probabilities of generating new infectives are found for k = 2, where the infectives have preferential probabilities p and q (p + q = 1) 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.