The theoretical influence of immunity between strain groups on the progression of drug-resistant tuberculosis epidemics.

BACKGROUND Emerging research suggests that genetically distinct strains of Mycobacterium tuberculosis may modulate the immune system differently. This may be of importance in high-burden settings where > or =1 genetic group of M. tuberculosis confers significant morbidity. METHODS A dynamic mathematical model was constructed to evaluate how different degrees of cross-immunity among M. tuberculosis groups could affect epidemics of drug-resistant tuberculosis (TB). RESULTS Simulated populations with immunogenically distinct TB strain groups experienced a heightened risk of drug-resistant TB, compared with populations without such strain diversity, even when the same rates of case detection and treatment success were achieved. The highest risks of infection were observed in populations in which HIV was prevalent. Drug-resistant strains with very low transmission fitness could still propagate in environments with reduced cross-immunity among different strain groups, even after common targets for case detection and treatment success are reached. CONCLUSIONS It is possible that the propagation of drug-resistant strains could depend not only on the rate of development of resistance and the fitness of the drug-resistant strains but, also, on the diversity of the strains in the region. The risk of infection with drug-resistant strains could be amplified in locations where there is reduced cross-immunity between originating strain groups. This amplification may be most profound during the first few decades of TB treatment expansion.