Wayne Getz Department Environmental Science, Policy & Management, University of California at Berkeley Modeling epidemics and disease invasion in heterogeneous populations: some new results on invasion and transmission with application to AIDS, SARS, and other infectious diseases Tuesday 30th November 12:05-12:55pm, Carslaw Lecture Theatre 173. A keystone in modeling epidemics is the formulation of appropriate transmission functions that include heterogeneity in contact rates among individuals reflecting differences in behavior (especially for sexually transmitted diseases) and daily exposure rates to other individuals. A characterizing statistic of epidemics has been, and continues to be, the value R0: the number of new (next-generation) infections expected per initial infection at the start of the epidemic. In this talk, I will present results from three recent studies: First, I will briefly review the fundamental differential equations of Kermack and McKendrick-the so-called SIR approach to epidemiological modeling-and show a mechanistic derivation of the classical frequency-dependent transmission, as well as modified forms incorporating behavior change, from fast pair-formation equations (see Lloyd-Smith, Getz, and Westerhoff, 2004). Then, I will discuss discretization of the Kermack-McKendrick equations and elaborations to investigate the efficacy of different control strategies in managing SARS epidemics (Lloyd-Smith, Galvani, and Getz 2003). Finally, I will discuss new results that use stochastic branching process theory to calculate properties of disease invasions when individual-level heterogeneity is considered (specifically, when individual force-of-transmission is assumed to be gamma-distributed), and show how uninformative R0 can be on its own in characterizing such properties (Lloyd-Smith et al., in prep). Lloyd-Smith, J.O., W. M. Getz, & H. V. Westerhoff, 2004. Frequency-dependent incidence in sexually-transmitted disease models: portrayal of pair-based transmission and effects of illness on contact behaviour. Proc Royal Soc. (Lond). B 271:625-634 Lloyd-Smith, J.O., A.P. Galvani, & W. M. Getz, 2003. Curtailing SARS transmission within a community and its hospital. Proc. Royal Soc. B. (Lond). 270:1979-1989 Lloyd-Smith, J.O., S. J. Schreiber, P. E. Kopp & W. M. Getz, in prep. Superspreading and the impact of individual variation on disease emergence.