Following primary tuberculosis (TB) infection, only approximately 10% of individuals develop active T.B. Most people are assumed to mount an effective immune response to the initial infection that limits proliferation of the bacilli and leads to long-lasting partial immunity both to further infection and to reactivation of latent bacilli remaining from the original infection. Infected individuals may develop active TB as a consequence of exogenous reinfaction, i.e., acquiring a new infection from another infectious individual. Our results in this paper suggest that exogenous reinfaction has a drastic effect on the qualitative dynamics of TB. The incorporation of exogenous reinfaction into our TB model allows the possibility of a subcritical bifurcation at the critical value of the basic reproductive number R0 = 1, and hence the existence of multiple endemic equilibria for R0 < 1 and the exogenous reinfaction rate larger than a threshold. Our results suggest that reducing R0 to be smaller than one may not be sufficient to eradicate the disease. An additional reduction in reinfaction rate may be required. These results may also partially explain the recently observed resurgence of TB. (C) 2000 Academic Press.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics