  \noindent We formulate an age-structured three-staged nonlinear partial
differential equation model that features {\it nonlinear} recidivism to the
infected ({\it infectious}) class from the {\it temporarily} recovered class.
Equilibria are computed, as well as local and global stability of the {\it
infection-free} equilibrium. As a result, a backward-bifurcation exists under
necessary and sufficient conditions. A generalized numerical framework is
established and numerical experiments are explored for two positive solutions
to exist in the {\it infectious} class.
