Abstract. Many models for the spread of infectious diseases in populations have been analyzed mathematically and applied to specific diseases. Threshold theorems involving the basic reprodu…
Abstract. Many models for the spread of infectious diseases in populations have been analyzed mathematically and applied to specific diseases. Threshold theorems involving the basic reproduction number [Formula: see text], the contact number [Formula: see text], and the replacement number [Formula: see text] are reviewed for the classic SIR epidemic and endemic models. Similar results with new expressions for [Formula: see text] are obtained for MSEIR and SEIR endemic models with either continuous age or age groups. Values of [Formula: see text] and [Formula: see text] are estimated for various diseases including measles in Niger and pertussis in the United States. Previous models with age structure, heterogeneity, and spatial structure are surveyed.