There are many different strains of TB. If there happen to be many strains circulating in a population, then individuals could be infected with more than one strain at a time which we define as mixed infection. This article focuses on the question whether mixed infection can explain the high prevalence of TB in some areas with overcrowding, low HIV prevalence and a high diversity in TB strains. The aim was to identify the factors that characterize mixed infection and investigate their impact on both the prevalence of TB and the proportion of mixed infection in these areas. To investigate the impact of these parameters, a mathematical model was developed for TB transmission dynamics that accounts for mixed infection.